It's specced as valve recession, and piston protrusion. Stuff you can measure easily.
It's actually hard to measure valve-to-piston clearance - not only do you need to assemble the head on the block, but you have to take into account the hydraulic lifters(which will take up the slack, and be at part lift with the engine running). Without an adjustable "solid" lifter for manually taking up the slack, you can't really do the job.