I agree, don't waste your time on stock gaskets that come with the headers, I don't care which brand. Get some coppers. Advantages of copper gaskets are: they can't tear, they can be reused (unless damaged by overtorquing), they are stronger, and you don't have to scrape gasket material when you remove them, which is a major PITA.
My buddy and I just got finished replacing the header gaskets on another friends '97 Z28, LT1 with longtubes, it took us two evenings and a couple ounces of blood. The guys that installed the headers in the first place used the one's that came with the Hooker Headers, which blew out like clockwork in 2 weeks. We put Mr. Gasket Coppers in there. I used SCE in mine. Everything is easy on a mustang compared to a LT1.