Not sure from the pic how or what your builder did with the measurements, but the correct thing to do is whether your using clay or play doh, is to clean the piston top, add the clay/paly doh, lighlty smear motor
oil on top of the clay so it won't stick to the valves and rotate the engine over..........then, with a razor blade, cut the clay in the middle of the valve relief and carefully remove one half of it, not disturbing the other half, then take your measurement on the thickness of the half left on the piston at the valve relief.............
You must always use solid lifters for this, regarless of what type of camshaft used in the motor......using hydraulic lifters will not give an accurate reading. Summitt/Jegs sells solid lifters in pairs just for this..
the best I can tell in the pic is the measurement was taken from the flat top of the piston????? if so, this measurement is useless and does not tell you anything about piston to valve clearance.
David