IF you do a search of this forum, you will learn that your choices are extremely limited. Assuming you have the 4.56 gears, you can get the pumpkin out of a 64-72 with 4.10 gears. A few 3.73s are out there, but about as scarce as hen's teeth.
Another option is to go with a later model differential, which is about 3.5" wider. Width is partially offset with newer rims which have more setback. With a 12 bolt, you can get 3.73 gears and still have a round housing. The bulletproof 14 bolt has a flat sided housing, but can be found with 3.42 gears. Cost around here for the 14 bolt is in the $300-350 range, 12 bolts are a lot cheaper.
