I made a poor man's stem height gage for Oldsmobile heads. The spec is 1.220 + - .005 for the top of the stem above the valve cover rail.
Setting the gage at 1.220. The bolt has a bevel and lines up with the center of the stem. The bevel there because the valves are not perpendicular to the cover surface.
Stem grinding on the valve grinder
Gage in use. The Olds 455 does not have an adjustable valve train so this height has to be right.