I dont know if anyone has ever asked this question, I cant seem to find it. I know bell housings and designs have changed over the years, but do all Dynaflows share the same external dimensions? Im asking the question because Ive never found a 100% answer to my idea. I want to swap another Nailhead into my 55 special, Ive found 364's and 401s reasonably priced, but they use a different bell housing. Then I read that you can swap the bell from a 57 only 364 Dynaflow onto the 55 Dynaflow, then Ive heard they bell is cast into the trans and cant be swapped. Then I started thinking, they improved the Dynaflow over the years maybe a later one from whatever donor car I choose would fit. But if the Trans is longer then I have to get a shorter torque tube and god only knows whats involved in that, or if the trans mount is in a different spot etc... So I was thinking we have a lot of smart guys on this board and to help my self and everyone else maybe we can compile a list of year to year differences. It would be nice if we could just look them up like a TH350 or 400 and know all the various measurements.