19.5" wheels will likely fit.
Check junk yards and look on step vans among other trucks.

Some info here, check the Accuride Catalog link and you'll find part numbers if you want to order new wheels.
http://www.stovebolt.com/techtips/wheels/

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-