spitfire header gasket question

Tried some old copper gaskets, they don't fit anything I own. Not sure what they fit.
These guys:
Mr. Gasket 7166MRG Mr. Gasket Copper Seal Header Gaskets

Not looking to tig up n grind the header flange to make stuff work unless it comes to that

Those mr gasket 358's are acrylic fiber. That sure doesn't sound hi temp to me!



Great advice again guys, I really do appreciate it! Making me think here. I can return the almost $30 Mr. Gaskets and get something else