Helen Bach
if it ain't Baroque ...
Panzerholz is interesting. If I ever returned to a Garrard (unlikely) I’d be very tempted to use a Panzerholz top-plate in a Lorricraft-style squash-ball decoupled plinth. I suspect that would work really well.
I’d be very interested to see a pic of where you ended up with Lenco plinth design.
There a lots of pics of Lenco/Panzerholz on the internet, showing excellent design, but maybe not so good too! And not only Lencos, I was commissioned by a dealer to design plinths for his SP10R turntables, I specified Permali products. There are a few 'do's and don'ts' with plinth design, but I'm willing to give advice, if needed. But you seem to have discovered the main criterion, thin (low mass) plinths, and I would only add the word 'damping'.
I would add the material Isophthalic polyester resin and granular bentonite. It can be cast, and is a lot less expensive than the engineered wood mentioned. At least one company makes (or used to make) these, run by a guy I used to work with. Wonder where he got the idea from? Again, a little advice is needed.