With the decomp lever engaged and piston at tdc push down on the rocker above the exhaust valve. There should always be some movement before the valve hits the piston.
At the end of the exhaust stroke where the intake valve begins to open is where my intake valve comes closest to the piston. Roll the engine through while pushing down on the valve. Make sure there is always some clearance.
My valve lash get bigger as the engine warms up. The cylinder gets hot and the push rods do not.
Thanks, Geno