You. If you're doing it yourself, what's the big deal to take it apart and see what's needed? With all the different input shafts, drums and pumps that could fit into a 904, you might have one of at least two that I can think of asfaras a two ring or three ring for openers. If the drum has a ring then the input shaft has to match I do believe. OTOH you could just change both, but then you'd have to change the pump as well. So...it might not be as simple as changing the shaft alone; and if you also have to change the drum (depending on what you have on hand) you will have to change the pump as well...at that point, maybe a later model trans with the ptk, since you might have to use so many parts from a donor trans and trash so many from your original trans. AND....maybe just sell your trans to somebody who needs one to fit their early size crank. They're kinda rare. At the risk of repeating myself...just don't want to proofread it again...