i want to swap out 700-r4 for th400,in a 90 suburban 4x4,what do i need to change?i know the trans are bolt in replacement what about the transfercase, i need a output shaft gear from a 241c that had a th400 ,what else?  

Why do you want to ditch the 700R4? It has a great first gear and overdrive too, Some years weren't so good, but you can get it rebuilt with an extra clutchband and I think a Corvette servo is recommended for better shifting. It might be better than swapping a TH400