Cory,
The originals were asbestos material which has become very hard to find now since all of the hooplah regarding that material. The originals were also flat across the top which also narrows the window on finding a concours quality replacements . I try to pick them up when I stumble across them but it is getting more difficult all the time. Cyclone was the original header manufacturer back then but bought gaskets from a gasket supplier ( usually "Best Gasket") like every other aftermarket header maker.
Randy