19.5" wheels are not original on an AD truck but they are a great upgrade. They came out about 1956 and were used for many years on some (certianly not all) 1 tons, step vans, NAPCO 1 ton trucks, and even on some similar ford trucks.
With 8R19.5 tires they're about 32" tall. That is a tad taller than 7.50-17 tires, helps with road speed, and nicely fills the fenders. Still a tall skinny tire look, many people don't notice they're non original.

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-