Hey Alexander,
Although I've never done it (yet) my educated guess would be a 3rd of 4th generation F-body,Camaro/Firebird,If you could find one with a 7.5 rear with disks you've got it made,get the rotors,calipers,brackets as much of the e-brake,cables etc.
floor mounted lever would be cool too if you have bucket seatsand no console,master cylinder and combination/proportioning valve and I think all that stuff could be adapted over to a G-body car and you've got the disc rear brakes the General never put on our cars! I imagine someone has done it somewhere so with a bit of serious googling you could probably find a conversion thread somewhere,maybe even here! I havn't searched for that one yet but I've though about it a bit because there for a while it was looking like the 81 was going to have a 7.5 untill the 9" became
affordable to me but now it looks like that very 7.5 is going to be in a 78 I've
aquired recently! Funny how life goes sometimes! KillerDave