My thinking is that 2 gaskets allow the two surfaces to fit tight to eliminate the potential for leaks just in case the block and the exhaust manifold surfaces are nopt perfectly parallel. Everything still bolts together with no problems and no leaks after 15 years. I also use stainless or bronze nuts with antiseize compound to make removal easy.
I have steel old style headers on mine and I use hi temp silicon on both side of the gasket. Never had one leak in many many years. Single asbestos or whatever gaskets. Dave
The Jalopy Journal
