I doubt it was down to the film... the different plastics of the ply shrinking or gassing at different rates - some early celluloid plates resemble thise 'Shrinky Dinkies' of the 80's
Dunno about increase sustain or tone... but i likes the engineering approach.
Although the internal threaded part looks quite short... but the height of a nut i spose.
I'm sure there are such things available from Spaldings (who i use for Stainless Dog Point Grub Screws for Bridge Saddles) or other Fastner shops.