Help!!! I am trying to figure out what kind of valve clearance I can get away with using stock style pistons and stock deck height with the old iron heads I have for my 1966 390 Ford motor. I need substantial lift as I will be campaigning this motor in a 65 Falcon bracket racing car. I am looking at cams in the .520 to .540 lift range, but don't know how to figure out if I'm going to be slapping my pistons with valves. I don't really want to order a cam if it won't work-soooo- I am trying to make peak torque between 4500 and 5500 rpm--any help greatly appreciated!