That was a B-61 Model Mack. They made almost everything except the tires.
I had a 673cu.in. Mack Diesel engine, practically the same design still used today.
Most had a two-stick "Duplex" 10-speed transmission, however you could get a 15-speed "Triplex" with two overdrive gears, or a 20-speed "Quadruplex," with three overdrives...no wonder there is not many around...
They made something like 46,000+ of them until the R-Model came out.