Welcome to the forum. Thanks for the post!
Your GS8 was built in January 1983. You can find it's 'Litter-Mate' here.
Bill Simmon has a GS9X #152. We always built guitars in multiples of six.
This is the second guitar I've seen with the X in the model number. I can't for the life of me remember what the X meant! I have opened up Bill 's guitar and looked around, I did notice resistors between the ground and volume pots.... This would, in concept, have extended the usable range on the volume pots, plus it let you turn up to eleven! Just kidding, sort of.
I have found a source for the Gibson/Schaller bridge, but have not ordered one to check them out.
Bill's guitar has a problem with the selector switch and I suspect that yours does also. If you are down to Burlington at some point, send me a PM/email. I can take a look at your's to be sure.