Based on what you said the unit is a 1970 ish model. Caterpillar bought Towmotor in 1969. There are no conversions available to convert from cushion to pneumatic tires or adding dual from cushion units. For yard work trucks are designed longer and wider to reduce the ground pressure.
This unit is designed to work on the inside or on smooth concrete surfaces outside period - no off roading.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.