i would give pacesetter a call, they have gaskets that would go between, the manifold and head or mani and cat. I suggest not to double up on the gaskets. that would just make way for air to leak over a period of time.
I will soon be making a gasket for the joint between my cat and FS Flex-Pipe.
The one that was on it got a Pinhole, which rapidly spread, and upon inspection of the gasket, it crumbled, so I'm looking at a "Copper"(Ultra or Something?) product that was referred to me by a racer who makes his own high-temp gaskets all the time.
It's like a paste which hardens, sort of like a PVC-type thing, only for really high temps.
i ahev all the gaskets i need. they are ford gaskets. the cat had 2 gaskets wraped with the cat on each end and the flex had 2 on one end and i ordered gaskets for before and after the flex, that came with 2 also. so i have the header gasket and 8 other gaskets for 3 joints!