Hi Jean,
This is my first post here, I'm a bit more active over on Lenco Lovers but I noticed Mario mentioned my name so I thought I'd join in. First off I'd just like to say thanks for inspiring me to rediscover the world of Lenco. A Gl72 was the first "separate" deck I owned way back but I was then seduced by the belt is better dogma of the 70's. An ebay listing by a guy selling a Garrard 401 which stated he was keeping his Lenco got me curious and a google led me to this thread. The rest as they say is history.
Anyway, down to business. I see we are both fans of the RS-A1 arm, a weird but wonderful contraption if ever there was one! I first heard it some years ago at a high end dealer not too many miles from where I live. Having recently bought one but not from that dealer he saw my posts on Lenco Lovers and emailed me with a few tips (they are not all bad) as he uses one himself. Firstly, they frequently use cartridges with threaded holes on the RS. Get the two lined up tight and screw the bolts in. I tried this and it worked fine. I suppose there is a chance that the two threads will be out of sync when you do this so maybe a tiny sliver of something compressible could be use between shell and cartridge if you can't get them up tight.
The other thing he told me I sort of knew, and I dare say you do to. The rotating headshell has nothing to do with an attempt to align the stylus tangentially like a parallel tracking arm but everything to do with decoupling the headshell from the arm. Alignment can look absurd if you watch this arm traverse a record but it works wonderfully!
Changing subjects, like many before me I have built fairly massive plinths using ply/mdf as per your recipe and been very happy with the results so I have no doubt that your even bigger, heavier plinths make for excellent vinyl replay. However, with a desire to make something less bulky and stimulated by various commercial but expensive manufacturers I have been trying out slate as a plinth material. I'm really quite excited with this material and have managed to make a small form 88 which to my ears sounds very fine indeed, so much so that I doubt if I will make another ply/mdf plinth. The plinth is about 44x40x25cm and weighs in at 45lbs or so.
See
Litle Stan I think it is a worthy alternative to the tried and trusted methods, so I suppose my question is have you thought about giving this material a go?
Regards, Ian