A GMC "B" Model. Interesting truck. Is it a 7500 Series? If it has a straight 5-Speed with no 2-Speed rear, it will drive a lot like a 237 Mack with a 5-Speed. It will be a "while" between shifts. That engine will have plenty of torque.
Bill
'60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan