Was it only the Skylarks and Cutlass's that went to the corporate 8.5 rear end in 71? If you do indeed have 2.73 gears and if that was NOT an 8.2 ratio, someone may have swapped an 8.5 rear in there. If thats the case you have the desireable 3 series carrier and can install your desired gears into it. Not to mention it is a good strong rear with plenty of parts to choose from as it was used from like 71 up till now I think. Another good thing about the A body 8.5 rears is they had bolt in axles unlike the newer ones that used c clips.
Holy crap I didnt realize this post was 2 years old, never mind pggto, im sure you have it worked out by now.
Thats some big time grave digging woody. As long as you are swapping the whole insides of the rear i think you should be fine, I dont think they made different axle housings for the different series carriers. You will need to use the same ring diameter carrier and gears though, you cant put a posi and gears from an 8.5 rear into an 8.2 rear end.
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1970 GTO 458 CID .040 over 4 Bolt 428 Block, Forged Eagle 455 Crank, 295 CFM SD KRE D-Ports, SD Old Faithful HR Cam + Comp HR Lifters, PPR Maxx-lite rods, Racetec pistons, PRW 1.65 SS Rockers, 900CFM Holley HP TBI, Performer RPM, Hooker Super Comps, 3" X-Pipe into 2.5" mufflers/tailpipes, 2.75 1st TH400, Continental 13" Converter, 8.5" 3.08 Posi.
Everything installed, fired up and tuning has begun!