Ring and Pinion

Hello guys i would like to knew what all parts i need for a ring and pinion installation i have installed a 3:23 now in a 8 3/4 center section with the 489 case and i have laying around some pinion and gears from 3:91, so my Question is do i need new bearings, shims ect... the center section was rebuild 2 years ago and i didnt drive much with that one

thx in advance Peter