Multi Part question

wow where to start
1: no rear disk brakes on A-bodies so no disk brakes on 8 3/4 rear UNLESS it is an aftermarket kit, if so you will need to contact the manufacturer of the kit, if it is a home made conversion we will need LOTS of pictures to try and figure out what you have and how to make it work, or you could just go back to drum brakes

2: if you are converting from a 7 1/4 to an 8 3/4, and it has no spring perches you will need to get some along with shock plates and U-bolts