Answers in reverse order...the Permatex 300 is fine for the cover. I would apply it to both sides of the gasket after cleaning the engine and cover very well. And I will emphasize the word "very." Please remember Permatex 300 (or even their Aviation Sealer) does not harden. I've taken off items that have been there for years successfully. Just remember to take it off slowly from a warm engine. I've had best luck with the thicker valve cover gasket...OR...as an alternative clean both the head and the valve cover very well and glue the thinner gaskets to each. Then install your cover with no sealer between the two gaskets. Although on the 216 I have seen this approach seep a bit so I suggest using sealer on both sides of the thicker gasket. Good luck!

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end