Billy - New master pins and new master bushings would be readily available from CavPower. You may have to gas-axe the old ones out, if they're broken.
The D339 is 831 cu in, and in the D7D it produces 140 FHP at a governed full load RPM of 1200. Maximum torque is at 800 RPM. You can lug these old engines down until you can nearly count the fan blades turning .. they're one of the original style, low RPM, high torque engines ..