I am under the impression that the th350 and 4 speed that came in these trucks are exactly the same length. the difference is in the transfer case/ Tranny adaptor only. Everything else including the drive shaft LENGTH is the same.
I don't know if this is 100% accurate or not but I'm sure some one will let me know If I'm mistaken...
You should be able to tell the th350 by the nearly square oil pan with one corner cut cleanly off. Look for the externally mounted vacuum modulator at the rear of the tranny. (It will be the size of a coffee cup) There are various tags on the th350s that will give you information so bring a good scraper.
I'm not sure how to tell you how to ID a 205, I just know what they look like. There’s a good pick of the rear of a 205 posted on another thread...
http://67-72chevytrucks.com/vboard/s...threadid=30203
There have been many other threads with great pics as well. Read back a few months, the 4X4 section is a low activity section of the board shouldn't be hard to find.
All years this setup was present will work ok. Hope that helps a little... Pete.