19.5" wheels from some types of Class A motorhomes will have the right bolt circle, but the tires that fit them are the same height as an 18" tube type tire. They will look way too small in the wheel wells of a truck that once ran 20" tube type tires. Like Ed says, those 10 hole 22.5" tubeless wheels that are the proper replacement for a 20" tube type are extremely scarce.
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!