Never found any original 67's with the OK on the valve cover. Don't believe they started that practice till the 68 production year. Sure you can find some "restored"
examples with them.
Most of the engine finish details are the same as the other plants since the engines were only assembled one place. Options and items installed on the engine at the individual plants could vary and often did depending on the part
Guess if your trying to get little paint mark details correct ALL of the other details on the car are 100% since if your worried about showing, in most classes paint marks are not required and will only, possibly be a source for deductions if they are incorrect. And all the paint marks in the world don't make up for having the wrong finish or part on an assembly that makes up the car.
Only crayon markings I've documented on the engine assembly itself would be the typically found number on the face of the drivers side head. Sometimes circled - depending on worker on shift that day assigned to that task what ever that was that they were documenting. Documented in red or white.
Exhaust manifolds may have also had paint marks but so few lasted (from the high temps) I'm only aware of those showing up on NOS manifolds
