Re: 55 Willys Pickup
The Blazer tranny should hook up fine to the transfer case, the TH350 and 400 were very compatable. You might have to do some firewall modifications though when switching from the Buick 350 to the Chevy 400.
I'm running the same Buick 350/TH400 setup you are and have been buying performace parts from TA Performance - might be worth a call and see what they have for a rebuilt TH400.
1953 Willys Pickup