These are factory tubeless 22.5” wheels from the late ‘50’s that were meant to be exact replacement to your 20” wheels, 5” wide. Tubeless tires started in ‘57 or so. Rare to non-existent. 19.5” wheels like this are available but look undernourished on a truck like yours. Other options exist that are more complex.

Ed
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'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.