I also have an unrestored 1938 unstyled WC single front wheel with 28 inch rear cast wheels. They are shaped like the 36 inch California special wheels, but these are 28 inch. I have never seen these anywhere else. They are listed in the parts book, but it doesn't list a part number for them.
I don't have any idea about production figures. The best reference book I have found is Allis-Chalmers: Farm Equipment 1914-1985 by Norm Swinford.