About the correct oitside diameter for tires on 19.5" rims.

Try 8X19.5, or better yet 8R19.5, they are around 33 or 34 inches, depending on the tire.

I think they look right on my truck, take a look for yourself.
http://www.stovebolt.com/gallery/mullen_grigg_1952.htm

And I had no problem finding tires, the same as on lots of RVs

•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-