426 Hemi Question

A friend and I was talking cars and he told me that he knew of a guy who put a 440 crank in a 426 hemi block with rods and used Hemi pistons. He said the motor ran fine and that the pistons was originally 13 to one and with this change it lowered it down to like 10 to 1. I have a hard time believing that this can be done so I am asking you .. The experts and why if you have any idea people do this? He may have been just messing with me.... So what say you all?