Regardless of who's gaskets you use, you have to look at the flange-to-head and mate up the gasket... to see IF it'll make physical contact and seal. Some headers, example Hooker 5115 Super comp (SB Mopar), have poor flanges with the factory welded beads not allowing contact with the gasket ports completely around their ports... NOTHING will then seal!... and you'll have to apply extra surface area of welding and or hi-temp JB Weld epoxy around the port so the gasket will have some contact.
The part of your statement I bolded is critical and often overlooked. But I'm not sure the hi temp JB will take that kind of heat on a prolonged basis. I know fel pro does sell the graphite / composite material in sheet form if you have to make your own as we have had to on occasion
