Hi John, Do you have any pictures of the Yuma #20? Sadly I did not take any pictures when I was there.
Also in the 1943 Canadian Massey advertising book showing the 81 and a plane on the cover list's a 21A combine as having steel wheels. Now I assume this was a war model.
Are you talking about a straight 21 Galvanized combine or a 21A?
And a picture just for kicks! These combines were used in a town 20 miles west of here and pictures are from the school I went to for a year. One of the #20's still sit about 12 miles from here.