Hmm, maybe I should be more clear... I mean that the output shaft is usually actually longer once the tail housing is OFF. So in otherwords to put a transfer case on the back of a 2wd transmission you would need a big fat spacer or to cut the output (tail) shaft shorter. Oh, and of course the speedometer output is on the transfer case on 4x4s.
Why do you ask, by the way? Thinking about a conversion to remedy a dead 2wd transmission?

I would not be surprised if there were other differences. On old th400's some have different spline counts as well.