Jumbo Steel Products of Azusa, California, produced a line of Simpson tractors from 1947 until 1952. These Simpson Jumbo tractors had a design heavily based upon the Custom tractor of Shelbyville, Indiana. Jumbo may have been licensed to produce the tractors for the western United States. The Simpson Jumbo tractors used Chrysler industrial engines. In 1952, the Jumbo Steel factory was sold to American Brake Shoe. The end of tractor production is listed variously between 1949 and 1955.
FarmCollectors.org - article on Custom Manufacturing