This is probably somewhat generic, but more than likely it was used as an aircraft tug or mowing rig on a flight line.
Since it has Air Force stenciling that could only be my guess. If you've ever been near a runway the grass is usually meticulously groomed. The base I work at now uses big New Holland tractors to mow and plow snow installation wide.
Was there an installation close to you? There were a few airports that were formerly Air Force bases and satellite installations.
If you were really into the history, the contract sounds like it was listed, if you wanted to find the record in the National Archives you might be able to find it still.