Some of your answers are in here
http://www.stovebolt.com/techtips/wheels/

In my opinion the best replacement wheels for your truck are 8 lug 19.5" tubeless wheels often found on GM step vans. they are out there but may take some searching.
When you get them some 8R19.5 tires are about right.

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-