I've built 4. Two with Source parts, two with factory cranks. If you're looking for mad torque, the 451 is basically a 440 bored .060 over. It's no slouch, but it should be headed and cammed like a 440. The source parts are good value but the rods should be cycled and then measured for size. The crank should be checked, and you'll have to give the bearings some chamfer because the crank filet's radius is too large for them. The Source crank drops in. I had one forged crank that cleared in the counterweight area (diameter of RB crank counterweights is about .200 larger than the B wedge block accepts in most cases...) with a few minor touches to the main saddles. And I had one that the crank had to be cut on a lathe to make the diameter smaller. As was mentioned... Good engines, but basically a lighter 440 performance wise.