I agree, they are rare. I recently found a 1956 one ton flat bed with what appear to be factory 19.5 wheels. The wheels have 1/2" lug bolts and use the same lug nuts as the 18" wheels. I tried to buy the truck, but the owner owns several old vehicles and apparently doesn't believe in selling, only buying.
Were the wheels tubeless type? The 19.5's I have are tubeless. Also, I finally dismounted one and they are exactly 8" backspace.
