That's a pretty common problem you have some pics of what you're dealing with. High-rise manifold sweep up in the runner areas and come in contact with valve covers sometimes and some grinding is needed so that the valve cover will sit down tightly and seal. I have also double gasket that area to solve the problem. For a little more money you can buy some thicker steel reinforced valve cover gaskets by moroso and that usually solves the problem but they run about 60 bucks. I just put a set of them on my 340 with my rocker arm change and I love them.