There is a critical brass bearing in the input shaft that has about .001 tolerance, have a buddy with a pin gauge to check it, if out of tolerance it requires replacement and reeming to size.
Not trying to hijack but, i'm doing one now and my input shaft has loose needle bearings in it held in place by a ring. Do the later transmissions have a one piece bearing? Mine is an A-body 3.09 non OD.