There are alot of variables that go into camshaft selection and proper valve clearance. For example, head selection plays a huge role. For example, trick flow heads have a different valve placement in the head that can only be used with matching pistons in some applications. Another factor is valve size, the standard 1.94 intake valve works with many of the aftermarket camshafts but changing to a 2.02 intake valve may cause clearance issues. Basically it comes down to your specific combination. You have to measure and verify you have the correct clearance on your motor. I had an F cam in my stock bottom end 302 with GT-40P heads and had no piston to valve issues, but your engine could have different tolerances, thinner head gasket, etc. that could cause it not to clear. the only way to find out for sure is to measure it on your application.