The intake valve is the only one that can possibly contact the piston. The exhaust valve is deeply recessed in the head, and at an angle that makes it impossible for it to touch the piston. With the head snugged down against the head gasket, not necessarily torqued, use a weak spring on the intake valve and lever it down against the piston top while measuring the valve travel with a dial indicator. Start doing this when the crankshaft is around 20 degrees before top dead center, and measure the valve-to-piston clearance every 5 degrees until you get to about 20 degrees after top dead center.
With those dimensions in hand (or on your computer memory) you can figure out what cam lift/head milling you can get away with. Don't let the valve get closer to the piston than .060" to allow for valve float, head gasket compression, etc. On one of the round track small block V8's we ran, the closest piston/valve clearance came at 20 degrees AFTER top dead center. The valve was outrunning the piston for the first few degrees of the intake stroke!
Jerry
