Just double checked the possibility of an old 20" wheel center being welded into a new 22.5" rim.
From what I can measure it looks like there is a slim chance of it working out. Difficult to tell if the back spacing can be made to work once you get the rim inside diameter and the center outside diameter to intersect.
If I had one of each in front of me I could probably get a better guess at it. From what I can see, the way they would intersect and have to be welded, is less than ideal for both looks and strength.

Best way to find out is to set one up in a vertical boring mill (or a big lathe) and start cutting.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-