V6 3 speed manual

AJ is right. Your original 3 speed is small, light duty and non-synchro first. (3.09 first gear) The bolt pattern is completely different than the A833 and the newer all syncho 3 speed that was introduced in 1970 or so. A 3 on the tree shifter is far from precise. It may be fine for puttin around town but terrible if you get in a hurry. Absolutely NO reason to consider using your original trans at all.

And after going to all that trouble, why a 3 speed? IMO, better to go 5 speed with OD right from the start.