Nailed it! You have very precisely described my SME plinth.
My grease-bearing Garrard 301 has the SME 3009 improved fixed head shell tone arm, and the Shure V15 Type III cartridge (hyper elliptical stylus). My dad gave it to me so it has sentimental value
I got given it when I was on a world business trip just after CDs came out, and just after my hifi was stolen. I bought Quad gear on that trip - pre-amp, amplifier and ESL-63 speakers - so hardly used the turn table.
The on-going debates on vinyl versus digital and the rising value of Garrard decks has piqued my curiosity. What is all the fuss about?
You mentioned start up speed - half a revolution - and they can stop just as quickly. I have replaced the main bearing with an oil bearing from the Classic Turntable Company.
I have kept the plinth as an outer shell and dustcover, but removed the flimsy base. It is now infilled with constrained layers of MDF on IsoAccoustics OREA Bordeau pucks sitting on 50-kg of Sydney sandstone. The deck springs are bypassed at the moment, but can be used for a comparison.
Thank you for the extra information!
UPDATE That makes sense. My dad originally housed the Garrard in a cabinet I designed and he built. The board in the SME plinth looks factory cut to me, from veneered chipboard! Could be my next upgrade. It is a pity SME cannot supply parts for these plinths!