Our trucks use 8 lugs on 6.5" bolt circle.

If your truck had 18" originally and you'd like to go back to that you'll be looking for old/used wheels.

For a modern equivalent tubeless wheel and tire look for 19.5" wheels and 8R19.5 tires are a good option. This is what I have on my 1 ton.

You may also fit some 16" wheels, check clearance on rear brake drums. Depending on the tire size they may or may not be as tall as you want.

•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-