Olds/Pontiac 9.3 in an A-Body?

I’m not sure if those axles were used in the eight lug in the Pontiac drum and wheel setup, but that might add some complications to your rear brake choices. The axles still used a five lug bolt pattern, and then the drum had the large eight bolt stud pattern near its outer perimeter. I don’t know if there’s a standard drum that will fit those shoes and backing plate, but I doubt it. IIRC, it seems like the dragster guys of the way back era outfitted the big Olds/Pontiac rear with disc brakes.