Head gasket thickness

If these are domed pistons, you need to clarify if only the dome is above the deck or is the flat quench area also above the deck. Maybe also post a picture at TDC. If it's a small dome and is intended for closed chamber heads like TFS 270s, and only the dome is protruding above the deck, then you'll have to mock up the head, without a gasket, turn it upside down, roll it over to TDC, loosen rod bolts, and measure how far the piston and rod can be moved toward the head. Once it stops, rock the piston back and forth, pivoting on the pin, and look for smallest reading. That's the piston to head clearance before gaskets are factored in. If the flat quench area of the piston is above the deck surface, mill the pistons as others have suggested.