I glue the thicker cork gasket to a leveled valve cover (first, punch the over-tightening deformations in the valve cover rim upwards) and use no seal between cork gasket and head.
Elongated flat washers were used with valve cover screws on my 54 and later 235/261 engines.
The washers look like this but they are symmetrical (left/right are symmetrical and top/bottom are symmetrical). I'll go out to my freezer (garage) and look for one, if anyone is interested.
