Fwiw: There are '71/72 A body 10 bolt 8.5s that came in non chevy cars that used bolt in axles in Olds, buick, not sure about Pontiac. The posi looked same as the chevy S spring unit. Same width as '68-'70 A body 12 bolt.
Also fwiw, I had a '73 A body [455 4 speed Cutlass "S"] with a 8.5 with bolt In axles.
On the '73-'77 A body rears, those will work in a "G" body, [and I assume '78-'81 A body]. They are MUCH wider, but the upper mounts work fine. You can narrow them easily, reusing the outer end and use "G" body axles from GN/442 [$250 ish a pair, summit], or, '62-'67 chevy II 28 spline axles from an 8.2".
You can also use 28 spline '88 up 2wd S-10 axles to make a narrower rear, about the same width as a stock vega rear.
p.s. - axle bearing is same for 7.5" 8.2", 8.5", 12 bolt car [some impala etc and trucks have a bigger wheel bearing]