I'm looking at a thumper cam from comp cams for my 18ft Rayson with a 383 chrysler with a holley single plane manifold and 750 carb. With the 107 overlap in the cam, I wonder about reverstion. Is there a check valve that can be used to prevent water from getting in the engine at low rpm? The exhaust is logs with over the transom pipes, not headers. I'll be using the boat for cruising and a few "hot runs" once in a while.