I think I can shed some light on the possible rim/drum clearance problems with tubeless tire rims. The 20" rims have straight centers because tube-type tires are installed with one rim side removed, then the split-rim flange is installed. Tubeless-tire rims need a drop center to allow the tire to be installed. I encountered this problem with a rear axle I installed on a Ford 1-ton from an early-model Chevy. The Ford used tubeless-type 16" tires, and the Chevy had 16" tube-type. The Ford wheels would not fit over the Chevy brake drums, so I wound up using tube-type rims on the inside, and tubeless outer wheels. It's very possible the newer rims you're having problems with are the result of the same type of brake drum mismatch I encountered.

BTW, the Ford is getting a Cummins turbo Diesel engine soon, and a New Process 4-speed transmission, so it's going to have a real identity crisis!
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!
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