If your engine is a stock MPI engine, reversion in the exhaust with any exhaust upgrade should be a non-happening item. How have you seen reversion issues and what is telling you that reversion is occuring? How is your full exhaust system configured from engine to tips?? I would like to see and hear about your use, camshaft size and type, exhaust system routing and plumbing as I suspect that something else is causing water to back up in the exhaust , not the header manifolds from Dana. Dana has sold I am sure hundreds of these header manifolds with a lot used on Merc EFI and MPI big blocks and you do not hear of them reverting water from the header itself in an engine application such as this appears to be. . Lets see if we can find your problem?
Ray @ Raylar