Piston to Valve clearance

Wazup guys , I just order a new cam kit at MOTORSPORT AUTO and they told me that I need to check the Piston to Valve clearance , now can anyone tell me how can I do this I have an idea how to do it , but I was hoping that someone have used the kind of cam I using , The setup that I have in my car is stock , stock pistons , its not been rebore , an E31 head L24 block . The cam is a 560 lift and 290 duration , Im taking my head to the machine shop so I can get a better or higher compression ratio than stock , now can anyone help me here I'll apreciated , thanks ...