F450 vs Ram 3500 DRW tow vehicle

You can increase an engine's displacement/torque by increasing bore, stroke, or number of pistons. The Cummins and Powerstroke are both 6.7 liter engines so will have similar cylinder pressure when they are making 1000 lbft of torque. Stroke vs bore makes no difference. Torque is a function of the fuel burned per revolution. Increasing the boost or the bore or the stroke puts more air in the cylinder to allow for more fuel to be injected. If you can burn 10% more fuel per revolution you should see about 10% more torque.