snack, the SME plinth is aluminum.
Atmasphere, I absolutely agree that the tonearm has to be rigidly connected to the main bearing but I'm not sure the arm board has to be exactly the same material. It certainly has to be rigid. Plain wood of any species is not a good choice because it is not dimensionally stable. However MDF Laminated with aluminum or a heavy plastic or solid surface material should be fine. You can even make the MDF harder by soaking it in Watco overnight.
Atmasphere, I absolutely agree that the tonearm has to be rigidly connected to the main bearing but I'm not sure the arm board has to be exactly the same material. It certainly has to be rigid. Plain wood of any species is not a good choice because it is not dimensionally stable. However MDF Laminated with aluminum or a heavy plastic or solid surface material should be fine. You can even make the MDF harder by soaking it in Watco overnight.