The Misalignment of the intake too the head of the engine is really bad in my opinion. I ran a H.O. motor with the pre HO "renix" intake for 5 months then I swapped in the H.O. intake, I could tell a very noticeable difference. I had a very noticeable power increase, better fuel mileage, and the sound of the exhaust was much louder. The louder exhaust had to do with the lack of air the engine was sucking in with the renix intake. You can use your old manifold but it will run much better with one that lines up correctly. People spend hundreds of dollars to get the head ports matched to the intake ports precisely for more power, even though they are lined up pretty close by the factory. I don't think you want a 1/4 inch lip sticking up blocking your airflow.