There seems to be a fair amount of confusion here so I'm going to try to help out...
1) TH400's have 6 bolts on the tail end, TH350's & TH700's have 4.
2) Spline counts:
(Pre '85 model / figure "8" bolt pattern)
TH400 = 32
TH350 / TH700 = 27
4spd = 10
('85 > / round bolt pattern )
Th400 = 32
4spd = 32
3) All of the tranny to t-case combos had unique adapters. If you want to mount a TH400 to a 4spd version 205 then you will need the correct adapter and then you have to deal with having the correct input/output shafts.
4) Making a 2wd tranny work on a 4wd application is certainly do-able, sometimes with no modifications. For TH400's there are 4 different tailshafts. Of these 4, the short shaft 2wd version with a bolt on yoke will work for a pre '85 TH400 version 205 t-case. The length is correct (I believe it sticks out of the case 4 1/2") so all you need is the correct adapter and a t-case with the short female 32 spline input (pre '85) shaft.
5) The 4spd case can be made to work with the TH400 but you will need to change the t-case input shaft (and get the correct adapter).
Take a look at my
WEBSHOTS ALBUM for examples of the rear of the TH400 case and the TH40/205 adapter. Also, the 205 tech section on the ORD website is very informative about the different 205 input shafts.
I hope this helps, if I missed anything let me know. /forums/images/graemlins/thumb.gif