A 19.5" tubeless tire has the same basic profile as an 18" tube type that was used on 1950s 1 ton dual rear wheel trucks. My 1959 3800 flatbed had 18" tube type wheels with 8 lug hubs. They're a little smaller than the 20" tube type tires used on the bigger rigs, but close. The19.5s with the 10 lug hubs are used on big motorhomes, so there are plenty of those tires available- - - -just a little pricey at times!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!