For your 36 project browse through www.4BTswaps.com, it is a forum for all types and brands of diesel engine conversions I think all of your listed engine choices have been discussed at one point or another and you can learn more about them by posting questions too.

Also check out oldGMCtrucks.com, a guy there is swapping a 6BT in an early GMC somewhat like yours. Really nice work.

My preference would be the 4BT in your truck, should fit better than the others and has reasonable power with easy upgrades if necessary.
If that's not enough HP it gets a lot more complicated to fit something with enough.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-