There are NO versions using early crystal glass. The game backglass was never intended to be made of glass. All backglasses (including the 'final stack' extras which around ~15 were made) were created using plexiglass. The second backup prototype (which was incomplete) was dismantled in early 1978 after Bally made the decision to not go forward with the development of production. The signs of the electronic SS era was just around the corner and most engineers and management were already beginning to prepare, although electronics were not yet completely ready.
The game project was initiated by Bally in 1975 as a means to use the last remaining potential of the EM era for profits. This is just a simple summary of a much more, extensive detailed history. Although I rarely log onto PinSide anymore, here is a small bit of additional information regarding Bigfoot (Bally, 1977) beyond what is presently recorded at the IPDB.