Are all B body rears interchangeable? I want posi for my 84 delta 88, and believe a cop caprice rear will fit, just wasnt sure. Any info?

 

If you are referring to a bubble caprice rear end, they are 1 and 3/8" longer at the pinion snout, so you would have to have your driveshaft shortened. The cop caprices, also have a different wheel bolt pattern. 5x5 instead of your 5x4.75"
Also, many of those came with disc brakes, and you would have to use the caprice brake proportioning valves and calipers.

They will fit, but with a lot of modifications.

 

yeah but didnt the box 9c1 caprice have a posi with the same dimensions?

 

The 90+ earlier Caprice 9C1 will still have the 8.5" 10 bolt rear, whcih means your current driveshaft will be too long due to the 8.5/10 pinion snout being longer than the 7.5/10. It will also have the 5x5" bolt pattern axles and big brakes.
On the plus side, they usually have a posi with 3.23 or 3.42 gears. Check before buying, though, since positraction was an option even on 9C1 cars and gearing can range anywhere from 2.73 to 3.42 depending on who ordered the car originally.

 

If your car's making any power, this is a swap you're really wanting to do. Careful, as some stockers were only 7-1/2" ring gears from the factory. My 77' Delta is is an 8-1/2 2.41 "C/G" axle, and was able to swap 3.73 posi guts from a 3.73 Camaro. Gotta know what you're doing though, or things can wear quick. Also went from a TH 350 to a 700R4 tranny, and had the driveshaft shortened, which was no big deal. Car now has a strongly built 455, vs the stock 403, and really goes. With 0.70 od lock up 4th, cruises about the same highway rpm as stock. This set up is really the cat's meow, and would highly recommend it.

 

I plan on finding an old 73-77 A body 8.5 rear and rebuilding it.

Will swap into a 80-85 B Body, but I'm going to be swapping in a posi rear and 30 spline axles dircetly from Moser. Also a girdle support cover, just for extra piece of mind. Uses the same drum brakesas the stock 7.5 rear, and the same bolt pattern (althought that really doesn't matter since I'm changing the axles anyway

J, feel free to comment on my plans

Sucks because I could have gotten a 76 Monte Carlo rear for $40. It was a 2.41 open. But I was looking for a posi and didn't know that the BBC of the day put out a whopping 245 HP and 200 ft/lbs