Yes Richard, you have the SME Plinth System l mentioned. You could buy all the parts separately. When l bought the 401 from a friend he had the deck mounted on a hi-fi bench with just the Perspex lid. As he was an electrical engineer he was able to order me just the base and counter spring hinges to make the full system.
All your descriptions confirm this…. sides progressively bigger from the base up. Four large rod spring adjusters with black knobs to level the sub-chassis in each corner. Silver trim 360 degrees around sides. Very heavy cover with counter balanced spring assembly to keep the lid up. Holes in the back for mains and RCA cables. It was a MONSTER and could creak at times (thick grease on spring bases fixed this).The sub-chassis did not bounce very much and was quite rigid. The 401 needed a really substantial plinth and this construction was the best option available. We now know solid granite or very heavy wooden bases do the job much better.
Everything is as you describe. There are always some on eBay in the UK as more were sold here of course. The classic Garrard set up in the early 70s in the UK was considered to be….
Garrard 401
SME 3009 or the 3009 improved
Shure V15 mkII or mkIII (or Goldring G800 or G850, but they didn’t track so well)
SME Plinth System.
There has always been a debate on which was the best of the two turntables. It comes down to personal choice in appearance or operational preference. Underneath there was little design difference. The 401 would clunk a lot using the twist start/stop control. The corner levers of the 301 were easier. BBC DJs would normally position the stylus half a revolution from the start of the track next to be played and the 301 was much easier to engage the motor and supposedly had quicker motor up to speed performance.
The BBC STORY
The 301 was the standard BBC radio turntable in the 60s and was the most loved by the pioneering DJs. The 401 was intended to replace these radio stations 301s as Garrard wanted to maintain this status of suppliers of said turntables.It backfired on Garrard as the DJs demanded that the 301s be retained and put back because the 401 was not so easy to use. The DJs preferred the controls and quicker take up speed performance of the 301. The batch of 401s l was told were re-boxed and then just chucked into a corner of a room somewhere. About 12 years ago someone was selling four mint 401s in their original boxes on eBay saying they did a BBC clearance on old gear that were ‘surplus to requirements’. I remembered all this and was able to tell the seller as to how they found their way there. I informed him of this story and he was selling each one far too cheaply (about £600 each) ……..l should have bought them all myself.
UPDATE
l don’t believe the SME Plinth System appeared until the 401 was in production so your model 301 was probably rehoused. SME would cut out the sub-chassis to your chosen turntable and SME arm model position if requested.