Now is your opportunity to look for the correct tire to replace your 20's with 22.5's, wheels are the problem. 22.5 wheels started coming out with the advent of tubeless tires, so look for late 50's trucks with these wheels, they will fit w/o having to bore them out. Look on farm trucks, 1.5 or 2 ton.

Ed

'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.