On my 383/496 motor with Stage VI heads, I use the pan evac from Moroso only. The diaphragm inside the breathers and check valve can get rusty and not work properly, you can put a vacuum gauge on the hose at the valve cover and check the amount of vacuum its actually pulling. I use the aluminum valley pan from Hughe's but have to trim to fit along with the front and rear support brackets, I do use Permatex Right stuff to seal all four contact area's, never had a leak making mid 9 seconds passes. I use a Edelbrock RB 440 intake with no spacers and that buys more room to use the aluminum valley pan.