diff --git a/devices/ioctrl/grandcentral.cpp b/devices/ioctrl/grandcentral.cpp
index cfad725..03e8b21 100644
--- a/devices/ioctrl/grandcentral.cpp
+++ b/devices/ioctrl/grandcentral.cpp
@@ -107,7 +107,7 @@ GrandCentral::GrandCentral() : PCIDevice("mac-io/grandcentral"), InterruptCtrl()
     this->escc->set_dma_channel(3, this->escc_b_rx_dma.get());
 
     // connect MESH (internal SCSI)
-    this->mesh = dynamic_cast<MeshController*>(gMachineObj->get_comp_by_name("MeshTnt"));
+    this->mesh = dynamic_cast<MeshController*>(gMachineObj->get_comp_by_name_optional("MeshTnt"));
     if (this->mesh == nullptr) {
         LOG_F(WARNING, "%s: Mesh not found, using MeshStub instead", this->name.c_str());
         this->mesh_stub = std::unique_ptr<MeshStub>(new MeshStub());
@@ -185,7 +185,10 @@ uint32_t GrandCentral::read(uint32_t rgn_start, uint32_t offset, int size)
         case 7: // VIA-CUDA
             return this->viacuda->read((offset >> 9) & 0xF);
         case 8: // MESH SCSI
-            return this->mesh->read((offset >> 4) & 0xF);
+            if (this->mesh)
+                return this->mesh->read((offset >> 4) & 0xF);
+            else if (this->mesh_stub)
+                return this->mesh_stub->read((offset >> 4) & 0xF);
         case 9: // ENET-ROM
             return ENET_ROM[(offset >> 4) & 0x7];
         case 0xA: // IOBus device #1 ; Board register 1 and bandit1 PRSNT bits
@@ -232,7 +235,11 @@ uint32_t GrandCentral::read(uint32_t rgn_start, uint32_t offset, int size)
             //LOG_F(WARNING, "%s: Unsupported DMA channel DMA_AUDIO_IN read  @%02x.%c", this->name.c_str(), offset & 0xFF, SIZE_ARG(size));
             return 0; // this->snd_in_dma->reg_read(offset & 0xFF, size);
         case MIO_GC_DMA_SCSI_MESH:
-            return this->mesh_dma->reg_read(offset & 0xFF, size);
+            if (this->mesh_dma) {
+                return this->mesh_dma->reg_read(offset & 0xFF, size);
+                break;
+            }
+            // fallthrough
         default:
             LOG_F(WARNING, "%s: unimplemented DMA register at 0x%X",
                   this->name.c_str(), this->base_addr + offset);
@@ -289,7 +296,10 @@ void GrandCentral::write(uint32_t rgn_start, uint32_t offset, uint32_t value, in
             this->viacuda->write((offset >> 9) & 0xF, value);
             break;
         case 8: // MESH SCSI
-            this->mesh->write((offset >> 4) & 0xF, value);
+            if (this->mesh)
+                this->mesh->write((offset >> 4) & 0xF, value);
+            else if (this->mesh_stub)
+                this->mesh_stub->write((offset >> 4) & 0xF, value);
             break;
         case 0xA: // IOBus device #1 ; Board register 1 and bandit1 PRSNT bits
         case 0xB: // IOBus device #2 ; RaDACal/DACula
@@ -348,8 +358,11 @@ void GrandCentral::write(uint32_t rgn_start, uint32_t offset, uint32_t value, in
             //this->snd_in_dma->reg_write(offset & 0xFF, value, size);
             break;
         case MIO_GC_DMA_SCSI_MESH:
-            this->mesh_dma->reg_write(offset & 0xFF, value, size);
-            break;
+            if (this->mesh_dma) {
+                this->mesh_dma->reg_write(offset & 0xFF, value, size);
+                break;
+            }
+            // fallthrough
         default:
             LOG_F(WARNING, "%s: unimplemented DMA register at 0x%X",
                   this->name.c_str(), this->base_addr + offset);
diff --git a/devices/ioctrl/macio.h b/devices/ioctrl/macio.h
index ffd494d..f2a9a95 100644
--- a/devices/ioctrl/macio.h
+++ b/devices/ioctrl/macio.h
@@ -183,7 +183,7 @@ private:
     Swim3::Swim3Ctrl*   swim3;      // floppy disk controller
 
     std::unique_ptr<DMAChannel>     curio_dma;
-    std::unique_ptr<DMAChannel>     mesh_dma;
+    std::unique_ptr<DMAChannel>     mesh_dma = nullptr;
     std::unique_ptr<DMAChannel>     snd_out_dma;
     std::unique_ptr<DMAChannel>     snd_in_dma;
     std::unique_ptr<DMAChannel>     floppy_dma;
diff --git a/machines/machinetnt.cpp b/machines/machinetnt.cpp
index 287d57e..eff4d53 100644
--- a/machines/machinetnt.cpp
+++ b/machines/machinetnt.cpp
@@ -61,11 +61,11 @@ int initialize_tnt(std::string& id)
     // attach IOBus Device #1 0xF301A000
     gMachineObj->add_device("BoardReg1", std::unique_ptr<BoardRegister>(
         new BoardRegister("Board Register 1",
-            0x3F                                        | // pull up all PRSNT bits
-            ((GET_BIN_PROP("emmo") ^ 1) << 8)           | // factory tests (active low)
-            ((GET_BIN_PROP("has_sixty6") ^ 1) << 13)    | // composite video out (active low)
-            (GET_BIN_PROP("has_mesh") << 14)            | // fast SCSI (active high)
-            0x8000U                                       // pull up unused bits
+            0x3F                                                                       | // pull up all PRSNT bits
+            ((GET_BIN_PROP("emmo") ^ 1) << 8)                                          | // factory tests (active low)
+            ((gMachineObj->get_comp_by_name_optional("Sixty6Video") == nullptr) << 13) | // composite video out (active low)
+            ((gMachineObj->get_comp_by_name_optional("MeshTnt") != nullptr) << 14)     | // fast SCSI (active high)
+            0x8000U                                                                      // pull up unused bits
     )));
     gc_obj->attach_iodevice(0, dynamic_cast<BoardRegister*>(gMachineObj->get_comp_by_name("BoardReg1")));
 
@@ -131,10 +131,6 @@ static const PropMap pm7500_settings = {
         new IntProperty( 0, vector<uint32_t>({0, 4, 8, 16, 32, 64, 128}))},
     {"emmo",
         new BinProperty(0)},
-    {"has_sixty6",
-        new BinProperty(0)},
-    {"has_mesh",
-        new BinProperty(1)},
     {"cpu",
         new StrProperty(
             cpu == PPC_VER::MPC601  ? "601" :
@@ -144,7 +140,7 @@ static const PropMap pm7500_settings = {
 };
 
 static vector<string> pm7500_devices = {
-    "Hammerhead", "Bandit1", "Chaos", "ScsiMesh", "MeshTnt", "GrandCentral", "ControlVideo", "Sixty6Video"
+    "Hammerhead", "Bandit1", "Chaos", "ScsiMesh", "MeshTnt", "GrandCentral", "ControlVideo"
 };
 
 static const MachineDescription pm7300_descriptor = {