The rumors about "split rims" abound- - - - -but there's only one style that's really dangerous. Those are the Firestone "RH-5" rims that come apart in the middle. They can be identified by an approximately 2 inch wide raised flat area in the middle of the barrel section of the rim. The rims that have either one or two pieces that form one side of the rim at the tire sidewall are safe to use and work on although some tire shops are still terrified of them.

The problem these days is finding tube type 20" or 22" tires- - - - -it seems the only place they're being made any more is China. Multi-piece rims cannot run tubeless tires, because they're not airtight. For every width 20" tire, there's usually a corresponding 22.5" tubeless, but that requires buying different wheels. Converting to disc brakes will probably be difficult and expensive- - - -there's nothing really wrong with properly maintained and adjusted drum brakes. Lots of big rigs still run them, and most any professional truck shop has no problem at all finding repair parts.
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!