A Body 833 or A Body 833OD?
sounds like a kool project,,, pretty strange both trannys you are considering have the 3.09 first gear,, i had a 65 B&T trans i converted to a slip yoke tail shaft,,easy to do,, u just have to make sure the donor trans for the tail shaft has the same size rear main bearing,, u have to switch the main shaft in the tail shaft as well as the housing,,
there is also a place that has a conversion U joint that is stronger the the ball and trunion and bolts right up to the trans 4 bolt flange if you dont convert to a slip yoke,,the trunion parts are hard to find new
