you have another option. Get a port flange like 1/8 thick and mill that portion down 1/8. Bolt that between the manifold and the head to give you another mounting surface. hit that area with a stone and get it flat so you can see where the low spots are. Ultra copper RTV works on exhaust flanges. I think you got enough to seal with only the manifold. dab some paint (zinc oxide) on a manifold and put it on and see where the paint hits.
