I used to have a problem with blowing out gaskets on the 460 in my 70 Cougar. I used the Percy's Seal-4-Good and they've been in there for at least 50,000 miles and 9 years.
Is a metal shim gasket what is appropriate for this application?
Not sure if you'd want to use an insulating type of gasket. The exhaust manifold is cooled by transfering it's heat to the head. Probably be best to do whatever possible to keep the exhaust from glowing red. I've seen enough bunrt up RV's on the side of the road.
Mark
Berkshire Transmissions
North Adams, Massachusetts