The big Chevy ain't nuthin to sneeze at if it's right. I did a quick look and don't see a 4.15 stroke piston for the 383......though I'm sure you can get one made. There are off the shelf pistons for a 4.250 stroke piston for the 383. That would give 482 cubes. With the 400 block, you'd have 503 cubes.
