I have a Keith Kraft stroked 428. I have been having trouble getting the valve cover gaskets to seal. I tried one cork gasket with high temp RTV just on the valve cover side and this did not work. Next I tried the same set up with RTV on both the gasket and the head, still did not seal correctly. Tried the rubber gasket and this was the worst situation. All of these were recommendations off of the search I performed here at Club Cobra. A friend of mine has built a couple of 390's and he recommended two Fel Pro cork gaskets, RTV both sides of the gaskets as well as the head (special attention to the area where the intake meets the head). I also used Mr. Gasket spreader bars for the two bottom bolts on the valve cover. I have not had any
oil leakage so far. Hope this will help
Coach Mike