I have been doing some work on my neighbor's Twin City and it has been converted to rubber from steel. After the wheels were sandblasted I noticed that the fronts said "Cleve Weld" on them and the rears "Firestone".  Who marketed the conversion kits the rubber companies or tractor manufacturers? This must have been quite the marvel when you could put rubber on a steel wheeled tractor. I assume most of the conversions took place after the war was over and there were no more rubber shortages. Sounds like a interesting article for the HPOCA magazine.
Steve Peterson