Tranny interchangeability

[Zachs55special]

Here's an advanced tech question for all the Buick Masters: I have a friend that has a '54 Special with a stick shift tranny, and he wants to know what year transmissions interchange with his. I have read on here before that the specials used a smaller tranny than the other models. His tranny has some problems with first and reverse (internal damage/wear) and we are looking for options in case his is unrepairable. The other thought we had in mind is putting a Dynaflow in it. I am technically capable of doing this, as an ASE certified mechanic, and long time customizer, and fabricator. We are exploring bolt in changes, verses major surgery. I.E.- will a '53 or '55 Dynaflow bolt to his driveshaft? (ya know, torque tube-) CARS lists the same basic torque ball gasket kit up through '55, so that logically should work, the spline configuration is my concern. And, naturally, what are the differences in bell housings,flexplates, etc., if any? Anybody done this? ---Zach