Swap out 7 1/4 RE for an 8 1/4 RE

Though not a strong as an 8 3/4 an 8 1/4 is still a stout rear end. If your power goal is less than 400 then there is no reason to not use it. Even if you goal is over 400HP it is easier to up grade than getting involved with cutting down housings, axles and moving spring perches.

Disk brakes on the front of an A-body is not an indicator of an 8 1/4 either. Slant 6 and 318 cars came with 7 1/4 rears even when they had disks as standard. It was optional on these cars and was standard starting in 73 on performance models when it replaced the 8 3/4.

Having a drive shaft shortened and balanced should cost between $50 and $75 at a local drive shaft shop.