Find a machine shop that has one of the old bench/belt sanders, they can sand them flat in about 10 min. should charge about $25 a manifold, sometimes they get wierd about the aluminum, we had a belt for doing aluminum...A cylinder head broach cutter will do an awsome job too, but expect to pay about $75 a manifold, (set-up is a bitch), then don't use gaskets, use something like Ultra copper from Permatex, works real good...
