I worked & managed a very large F body GM & musclecar salvage yard for 6 years
We built a bunch of low budget Hot Rods & fast street cars
We had a pile of different brake rotors The bolt pattern doesn't really matter You drill a new pattern or elongate what pattern you have

The composite rotors on the newer stuff 90's & up is a great place to look go to your local JY with a caliper or a tape & the axle or find your same axle there & find what's the closest match
I've done a bunch of low budget rear disc on just about every rearend made using salvage yard parts