I would suggest a 30 spline output shaft. Make sure it is an A-Body trans. I swap to the early, without a Vin Pad, standard cast iron 307 front bearing main case in any O/D I'm going to run in one of my cars. Pictures for reference. Passon Performance has them as well. Pull the side cover and look for damage. Get Passon's book on rebuilding 4 speeds, Chrysler A-833 Transmissions — How to Rebuild and Modify . That will familiarize you with the different combinations.