I am going to venture this is not a Bush Hog brand name. I have seen a unit made by Sidewinder that for the drive mechanism used 3 mounted tires. The PTO shaft turned one tire which by friction turned the other two each attached to a spindle. This fits their MO of not using a standard gear box. Sidewinder is just a guess.
In the 50's and 60's shredders were home made using truck rear ends for lack of tractor PTO. I'm going to venture that as built in the 70's.