Overlap is what affects pisto valve clearance, valve lift is not the factor. When the intake valve is fully open the piston is already traveling down the bore drawing the intake charge in, the only way to tell is check, dont listen to anyone when it comes to piston to valve clearance. Copy and paste this for 2 methods, heads on and heads off method http://sbftech.com/index.php/topic,57.0.html
Good overall article. When specifying the clearance needed for the intake and exhaust valves in the "feeler gauge" portion the values got reversed, calling for more clearance on the intake and less on the exhaust. That second method is what I use but with a dial indicator on the spring retainer instead of feeler gauges. I measure at 5* increments from 20* BTDC to 20* ATDC to find the closest interference point.
BTW, the last engine I did had TRW (Speedpro) forged pistons. With my cam there was not enough valve relief for 2.02 valves, had to enlarge the reliefs.
Exhaust valve is most critical - you have the valve opening as the piston comes up to expel gasses. Make a mistake and you slap the valve as the cam is trying to open it.
I double checked mine, even after the first test showed we had plenty of clearance. You also might want to consider degreeing your whole cam if you're going to be running one that causes valve interference. It'd be a shame to get a mis-machined cam and bend a couple of valves.