diff --git a/pkg/cmd/roachtest/cluster_test.go b/pkg/cmd/roachtest/cluster_test.go
index fcab21c2b325..451c98cc7cae 100644
--- a/pkg/cmd/roachtest/cluster_test.go
+++ b/pkg/cmd/roachtest/cluster_test.go
@@ -319,15 +319,15 @@ func TestAWSMachineType(t *testing.T) {
 
 	for _, tc := range testCases {
 		t.Run(fmt.Sprintf("%d/%s/%t/%s", tc.cpus, tc.mem, tc.localSSD, tc.arch), func(t *testing.T) {
-			machineType, selectedArch := spec.AWSMachineType(tc.cpus, tc.mem, tc.localSSD, tc.arch)
+			machineType, selectedArch := spec.SelectAWSMachineType(tc.cpus, tc.mem, tc.localSSD, tc.arch)
 
 			require.Equal(t, tc.expectedMachineType, machineType)
 			require.Equal(t, tc.expectedArch, selectedArch)
 		})
 	}
 	// spec.Low is not supported.
-	require.Panics(t, func() { spec.AWSMachineType(4, spec.Low, false, vm.ArchAMD64) })
-	require.Panics(t, func() { spec.AWSMachineType(16, spec.Low, false, vm.ArchARM64) })
+	require.Panics(t, func() { spec.SelectAWSMachineType(4, spec.Low, false, vm.ArchAMD64) })
+	require.Panics(t, func() { spec.SelectAWSMachineType(16, spec.Low, false, vm.ArchARM64) })
 }
 
 func TestGCEMachineType(t *testing.T) {
@@ -413,7 +413,7 @@ func TestGCEMachineType(t *testing.T) {
 
 	for _, tc := range testCases {
 		t.Run(fmt.Sprintf("%d/%s/%s", tc.cpus, tc.mem, tc.arch), func(t *testing.T) {
-			machineType, selectedArch := spec.GCEMachineType(tc.cpus, tc.mem, tc.arch)
+			machineType, selectedArch := spec.SelectGCEMachineType(tc.cpus, tc.mem, tc.arch)
 
 			require.Equal(t, tc.expectedMachineType, machineType)
 			require.Equal(t, tc.expectedArch, selectedArch)
diff --git a/pkg/cmd/roachtest/spec/cluster_spec.go b/pkg/cmd/roachtest/spec/cluster_spec.go
index 7445ce35c3e8..2039bd827f71 100644
--- a/pkg/cmd/roachtest/spec/cluster_spec.go
+++ b/pkg/cmd/roachtest/spec/cluster_spec.go
@@ -65,11 +65,14 @@ type ClusterSpec struct {
 	// TODO(#104029): We should remove the Cloud field; the tests now specify
 	// their compatible clouds.
 	Cloud string
-	Arch  vm.CPUArch // CPU architecture; auto-chosen if left empty
-	// TODO(radu): An InstanceType can only make sense in the context of a
-	// specific cloud. We should replace this with cloud-specific arguments.
-	InstanceType string // auto-chosen if left empty
-	NodeCount    int
+
+	// TODO(radu): defaultInstanceType is the default machine type used (unless
+	// overridden by GCE.MachineType or AWS.MachineType); it does not belong in
+	// the spec.
+	defaultInstanceType string
+
+	Arch      vm.CPUArch // CPU architecture; auto-chosen if left empty
+	NodeCount int
 	// CPUs is the number of CPUs per node.
 	CPUs                 int
 	Mem                  MemPerCPU
@@ -93,12 +96,14 @@ type ClusterSpec struct {
 
 	// GCE-specific arguments. These values apply only on clusters instantiated on GCE.
 	GCE struct {
+		MachineType    string
 		MinCPUPlatform string
 		VolumeType     string
 	}
 
 	// AWS-specific arguments. These values apply only on clusters instantiated on AWS.
 	AWS struct {
+		MachineType string
 		// VolumeThroughput is the min provisioned EBS volume throughput.
 		VolumeThroughput int
 	}
@@ -106,7 +111,7 @@ type ClusterSpec struct {
 
 // MakeClusterSpec makes a ClusterSpec.
 func MakeClusterSpec(cloud string, instanceType string, nodeCount int, opts ...Option) ClusterSpec {
-	spec := ClusterSpec{Cloud: cloud, InstanceType: instanceType, NodeCount: nodeCount}
+	spec := ClusterSpec{Cloud: cloud, defaultInstanceType: instanceType, NodeCount: nodeCount}
 	defaultOpts := []Option{CPU(4), nodeLifetime(12 * time.Hour), ReuseAny()}
 	for _, o := range append(defaultOpts, opts...) {
 		o(&spec)
@@ -257,31 +262,42 @@ func (s *ClusterSpec) RoachprodOpts(
 
 	createVMOpts.GeoDistributed = s.Geo
 	createVMOpts.Arch = string(arch)
-	machineType := s.InstanceType
 	ssdCount := s.SSDs
 
+	machineType := s.defaultInstanceType
+	switch s.Cloud {
+	case AWS:
+		if s.AWS.MachineType != "" {
+			machineType = s.AWS.MachineType
+		}
+	case GCE:
+		if s.GCE.MachineType != "" {
+			machineType = s.GCE.MachineType
+		}
+	}
+
 	if s.CPUs != 0 {
 		// Default to the user-supplied machine type, if any.
 		// Otherwise, pick based on requested CPU count.
 		var selectedArch vm.CPUArch
 
-		if len(machineType) == 0 {
+		if machineType == "" {
 			// If no machine type was specified, choose one
 			// based on the cloud and CPU count.
 			switch s.Cloud {
 			case AWS:
-				machineType, selectedArch = AWSMachineType(s.CPUs, s.Mem, s.PreferLocalSSD && s.VolumeSize == 0, arch)
+				machineType, selectedArch = SelectAWSMachineType(s.CPUs, s.Mem, s.PreferLocalSSD && s.VolumeSize == 0, arch)
 			case GCE:
-				machineType, selectedArch = GCEMachineType(s.CPUs, s.Mem, arch)
+				machineType, selectedArch = SelectGCEMachineType(s.CPUs, s.Mem, arch)
 			case Azure:
 				machineType = AzureMachineType(s.CPUs, s.Mem)
 			}
-		}
-		if selectedArch != "" && selectedArch != arch {
-			// TODO(srosenberg): we need a better way to monitor the rate of this mismatch, i.e.,
-			// other than grepping cluster creation logs.
-			fmt.Printf("WARN: requested arch %s for machineType %s, but selected %s\n", arch, machineType, selectedArch)
-			createVMOpts.Arch = string(selectedArch)
+			if selectedArch != "" && selectedArch != arch {
+				// TODO(srosenberg): we need a better way to monitor the rate of this mismatch, i.e.,
+				// other than grepping cluster creation logs.
+				fmt.Printf("WARN: requested arch %s for machineType %s, but selected %s\n", arch, machineType, selectedArch)
+				createVMOpts.Arch = string(selectedArch)
+			}
 		}
 
 		// Local SSD can only be requested
diff --git a/pkg/cmd/roachtest/spec/machine_type.go b/pkg/cmd/roachtest/spec/machine_type.go
index 8239ae522599..93a8e9a9017c 100644
--- a/pkg/cmd/roachtest/spec/machine_type.go
+++ b/pkg/cmd/roachtest/spec/machine_type.go
@@ -28,7 +28,7 @@ import (
 //
 // At the time of writing, the intel machines are all third-generation Xeon, "Ice Lake" which are isomorphic to
 // GCE's n2-(standard|highmem|custom) _with_ --minimum-cpu-platform="Intel Ice Lake" (roachprod's default).
-func AWSMachineType(
+func SelectAWSMachineType(
 	cpus int, mem MemPerCPU, shouldSupportLocalSSD bool, arch vm.CPUArch,
 ) (string, vm.CPUArch) {
 	family := "m6i" // 4 GB RAM per CPU
@@ -118,7 +118,7 @@ func AWSMachineType(
 // At the time of writing, the intel machines are all third-generation xeon, "Ice Lake" assuming
 // --minimum-cpu-platform="Intel Ice Lake" (roachprod's default). This is isomorphic to AWS's m6i or c6i.
 // The only exception is low memory machines (n2-highcpu-xxx), which aren't available in AWS.
-func GCEMachineType(cpus int, mem MemPerCPU, arch vm.CPUArch) (string, vm.CPUArch) {
+func SelectGCEMachineType(cpus int, mem MemPerCPU, arch vm.CPUArch) (string, vm.CPUArch) {
 	series := "n2"
 	selectedArch := vm.ArchAMD64
 
diff --git a/pkg/cmd/roachtest/spec/option.go b/pkg/cmd/roachtest/spec/option.go
index d28ed50a6773..4443122f5266 100644
--- a/pkg/cmd/roachtest/spec/option.go
+++ b/pkg/cmd/roachtest/spec/option.go
@@ -198,6 +198,13 @@ func RandomlyUseZfs() Option {
 	}
 }
 
+// GCEMachineType sets the machine (instance) type when the cluster is on GCE.
+func GCEMachineType(machineType string) Option {
+	return func(spec *ClusterSpec) {
+		spec.GCE.MachineType = machineType
+	}
+}
+
 // GCEMinCPUPlatform sets the minimum CPU platform when the cluster is on GCE.
 func GCEMinCPUPlatform(platform string) Option {
 	return func(spec *ClusterSpec) {
@@ -212,6 +219,13 @@ func GCEVolumeType(volumeType string) Option {
 	}
 }
 
+// AWSMachineType sets the machine (instance) type when the cluster is on AWS.
+func AWSMachineType(machineType string) Option {
+	return func(spec *ClusterSpec) {
+		spec.AWS.MachineType = machineType
+	}
+}
+
 // AWSVolumeThroughput sets the minimum provisioned EBS volume throughput when
 // the cluster is on AWS.
 func AWSVolumeThroughput(throughput int) Option {
diff --git a/pkg/cmd/roachtest/test_registry_test.go b/pkg/cmd/roachtest/test_registry_test.go
index bf19ef33c6db..aa42782fe79f 100644
--- a/pkg/cmd/roachtest/test_registry_test.go
+++ b/pkg/cmd/roachtest/test_registry_test.go
@@ -32,7 +32,6 @@ func TestMakeTestRegistry(t *testing.T) {
 		s := r.MakeClusterSpec(100, spec.Geo(), spec.Zones("zone99"), spec.CPU(12),
 			spec.PreferLocalSSD(true))
 		require.EqualValues(t, 100, s.NodeCount)
-		require.Equal(t, "foo", s.InstanceType)
 		require.True(t, s.Geo)
 		require.Equal(t, "zone99", s.Zones)
 		require.EqualValues(t, 12, s.CPUs)
@@ -40,13 +39,11 @@ func TestMakeTestRegistry(t *testing.T) {
 
 		s = r.MakeClusterSpec(100, spec.CPU(4), spec.TerminateOnMigration())
 		require.EqualValues(t, 100, s.NodeCount)
-		require.Equal(t, "foo", s.InstanceType)
 		require.EqualValues(t, 4, s.CPUs)
 		require.True(t, s.TerminateOnMigration)
 
 		s = r.MakeClusterSpec(10, spec.CPU(16), spec.Arch(vm.ArchARM64))
 		require.EqualValues(t, 10, s.NodeCount)
-		require.Equal(t, "foo", s.InstanceType)
 		require.EqualValues(t, 16, s.CPUs)
 		require.EqualValues(t, vm.ArchARM64, s.Arch)
 	})
diff --git a/pkg/cmd/roachtest/tests/admission_control_database_drop.go b/pkg/cmd/roachtest/tests/admission_control_database_drop.go
index 2cc65ea03967..062677d00911 100644
--- a/pkg/cmd/roachtest/tests/admission_control_database_drop.go
+++ b/pkg/cmd/roachtest/tests/admission_control_database_drop.go
@@ -36,15 +36,15 @@ func registerDatabaseDrop(r registry.Registry) {
 		spec.Cloud(spec.GCE),
 		spec.GCEMinCPUPlatform("Intel Ice Lake"),
 		spec.GCEVolumeType("pd-ssd"),
+		spec.GCEMachineType("n2-standard-8"),
 	)
-	clusterSpec.InstanceType = "n2-standard-8"
 
 	r.Add(registry.TestSpec{
 		Name:             "admission-control/database-drop",
 		Timeout:          10 * time.Hour,
 		Owner:            registry.OwnerAdmissionControl,
 		Benchmark:        true,
-		CompatibleClouds: registry.AllExceptAWS,
+		CompatibleClouds: registry.OnlyGCE,
 		Suites:           registry.Suites(registry.Weekly),
 		Tags:             registry.Tags(`weekly`),
 		Cluster:          clusterSpec,
diff --git a/pkg/cmd/roachtest/tests/admission_control_index_backfill.go b/pkg/cmd/roachtest/tests/admission_control_index_backfill.go
index 7127978c9df2..991e8f4ab067 100644
--- a/pkg/cmd/roachtest/tests/admission_control_index_backfill.go
+++ b/pkg/cmd/roachtest/tests/admission_control_index_backfill.go
@@ -37,15 +37,15 @@ func registerIndexBackfill(r registry.Registry) {
 		spec.Cloud(spec.GCE),
 		spec.GCEMinCPUPlatform("Intel Ice Lake"),
 		spec.GCEVolumeType("pd-ssd"),
+		spec.GCEMachineType("n2-standard-8"),
 	)
-	clusterSpec.InstanceType = "n2-standard-8"
 
 	r.Add(registry.TestSpec{
 		Name:             "admission-control/index-backfill",
 		Timeout:          6 * time.Hour,
 		Owner:            registry.OwnerAdmissionControl,
 		Benchmark:        true,
-		CompatibleClouds: registry.AllExceptAWS,
+		CompatibleClouds: registry.OnlyGCE,
 		Suites:           registry.Suites(registry.Weekly),
 		Tags:             registry.Tags(`weekly`),
 		Cluster:          clusterSpec,
diff --git a/pkg/cmd/roachtest/tests/restore.go b/pkg/cmd/roachtest/tests/restore.go
index bafe60bc7050..564f75fa50cc 100644
--- a/pkg/cmd/roachtest/tests/restore.go
+++ b/pkg/cmd/roachtest/tests/restore.go
@@ -537,13 +537,13 @@ func (hw hardwareSpecs) makeClusterSpecs(r registry.Registry, backupCloud string
 	}
 	s := r.MakeClusterSpec(hw.nodes+addWorkloadNode, clusterOpts...)
 
-	if backupCloud == spec.AWS && s.Cloud == spec.AWS && s.VolumeSize != 0 {
+	if backupCloud == spec.AWS && s.VolumeSize != 0 {
 		// Work around an issue that RAID0s local NVMe and GP3 storage together:
 		// https://github.com/cockroachdb/cockroach/issues/98783.
 		//
 		// TODO(srosenberg): Remove this workaround when 98783 is addressed.
-		s.InstanceType, _ = spec.AWSMachineType(s.CPUs, s.Mem, s.PreferLocalSSD && s.VolumeSize == 0, vm.ArchAMD64)
-		s.InstanceType = strings.Replace(s.InstanceType, "d.", ".", 1)
+		s.AWS.MachineType, _ = spec.SelectAWSMachineType(s.CPUs, s.Mem, s.PreferLocalSSD && s.VolumeSize == 0, vm.ArchAMD64)
+		s.AWS.MachineType = strings.Replace(s.AWS.MachineType, "d.", ".", 1)
 		s.Arch = vm.ArchAMD64
 	}
 	return s