For a 1/2 ton the 4bt sounds like a great choice to me.
lots and lots of info and folks happy with their 4bt conversions over at www.4btswaps.com
stop by and have a look.

A 6bt is a fair amount of weight and not quite as simple of a swap in a small truck.

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
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-