curious about valve lash setting/check

Makes sure that surface isn't warped from overtightening , might surprise you .
A slight pain int e a-- to do, but u could chuck the therm. cover up in a lathe and turn the gasket surface down about .060ish , quiting at the inside of the bolt holes. Creating a raised surface around the big water hole for the gasket to bite/smash better.
Bob, I couldn't see it with a straight edge, but as soon as I started taking material down, sure enough, bowed from hole to hole. thank you, got it cleaned up.