Rear end swap

Okay lacking a little about what you have but here goes.
What rear end do you currently have in your car?
If you have the 7.25 rear, they also made a 7.25 big bolt pattern axle as well
If you have the 8.75 (unless you're going to a Dana, why do you want swap it?) just call dr. Diff and order a set of BBP axle for it.

If you have the 7.25 rear and are looking for an upgrade, just get the 8.25 rear out of a 73+ A body. These will be BBP already but do know they come in two different forms depend on the gears inside, the housing is different. Try to get one the has at least 2.91(or num higher) this way you can go to the local junkyard find a 96 or older jeep grand Cherokee and pull the better gear and limited slip unit and install it into the A body 8.25 rear. If the jeep also has rear disc brakes take those as well because it's bolt on deal for the 8.25 rear!