Mr Gasket ultraseal works for me. Glue them to the cover with 3m trim adhesive(gorilla snot). Use nothing on head side.
With factory stamped steel valve covers, glue is the ticket. And don't over tighten. When new, tighten reasonably; then after a heat cycle do final tightening.
I tend to use Felpro cork/rubber combo, and they work great. I think the ones on my street Cuda 440 are at least 7 years old...
My current Daytona "tow truck" engine has factory valve covers and factory iron heads and they don't leak at all.
