I would stay with the original rear and upgrade if needed/wanted.

In addition to monaz's post.
For HP, stock 12 bolts are over rated unless you spend alot to make'm strong.
The pinions are smaller then mid 70's TA 10 bolts.
The axle's are only held in with small c-clips.
Not bolted to the flange like Pontiac's are.
If a clip breaks, out comes the axle.
Most everyone has "c-clip" eliminators installed. Not a novice procedure.
If thats been done, and theres nothing wrong with it, $300's a steal.