I have a 77k20 and was wondering how to tell the difference from a th350 and th400, also I was wondering how to tell that t-case is in the truck.
Any help is appreciated, thanks  

Looking at the pan of the transmission, the TH350 is mostly square with the right rear corner cut at a 45* angle; the pan of the TH400 is an odd shape (hard to describe).
You can tell transfer case just by looking at the shift patern.  The NP203 (full time case) is H-loc,H,N,L,L-loc; the NP205 (part time case) is 4-hi,2-hi,N,4-low.  If you can't tell by that you will have to look under the truck at the case.  The NP203 is almost twice the size of the NP205 because of the differential in the NP203.  I know one of these magazines have an article with pictures of transfer cases within the past couple years.