If you go with having a 22.5" wheel made, I would use a 22.5 x 6.75 wheel rim. I know Wheels Now has a 22.5 x 6.75 rim option.

That would be perfect for the 9R/22.5 radial tire. The 9R/22.5 is considered a good replacement for the original 8.25/20 bias ply tire. The diameters are both ~38 inches.
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-David

1953 2-Ton GMC

I'm a machinist... because engineers need heroes too.