What your describing is a model 12 grader called them knuckle buster all the control levers seemed /felt like you were engaging a gear driven control instead of more modern all hydraulic controls . I was around them years ago but ours didnt have a PONY motor to start them but were electric starter our cat d8 cable blade had the pony motors and had the cup with spring loaded lid you put your either ball in on the intake. Try finding an either ball today. I would just treat it as a 12 for repair the numbers on the cat graders ment how long the molboard (blade) was 12 12ft a 120 is 120 inches long all the way up to 26 and yea 26 ft wide blade a monsterRecently purchased in less than operating condition. Has a military specific serial number different prefix versus civilian model. Being i work for Caterpillar I have access to most anything information wise. We have a guide that converts military to civilian in most cases it is correct. The machine serial number is 90R00137, guide states a 13U civilian is equivalent, close but needing help. No M designation on the US Army data plate. No luck in searching for publications online. Anyone have a book stashed or the number for the publication?