Well, I finally tore into the project today. I only had to drill out and retap 3 bolt holes. The manifold checked out nice and flat when I checked it with a straightedge. Since the gasket set included the one that goes between the manifolds for the heat riser, I took them apart and reassembled them to the engine before tightening anything. Everything went together well and it runs quieter than ever. I'll let you know in a few weeks how well it holds up.