Valve clearance is going to depend on the combustion chamber size, duration and amount of valve lift with the camshaft being used, valve head diameter and the amount of valve relief in the pistons. This can be determined by using a strip of modeling clay (No Play-dough, it contains salt) placed on the piston where the valves will be closest to the piston. Installing a used and compressed head gasket and installing the head. The engine rotated slowly, by hand, two complete revolutions (Rotated slowly, you don't want to damage anything if there is interference.), and then the head removed and the thickness of the clay measured where the valves have left an impression. You should have at least .080" intake and .100" exhaust clearance at TDC between the piston and the valves.
This is the only sure way of knowing the amount of clearance that you will have. If reliefs need to be cut, it's best done by a machine shop and the pistons will need removal.
There is a method where a cutter is installed in the cylinder head, in place of the valve, and the cuts made without piston removal, but the cutter is expensive and is best done by someone familiar with this method. You may be OK with the pistons that you currently have. | 
