The head of the bolts press against the convex side of the washers....concave side against the manifold. Look for a sealant with high temp specs. I believe Permatex, KW, Felpro, and probably a few others have them. I've used some Permatex Hi-temp RTV, KW Coppercoat, and Felpro Hi-Tac with good success depending on the application.
