a body rear end ? 8 3/4 vs dana 60

It would be important to know if you are using a Torqueflite or a manual trans.

Chrysler put Dana 60's in 440, 440 6-Bbl and Hemi cars with 4-speeds including
the original '68 SS/B (then) Darts and Barracudas. Automatic cars got the 8-3/4.