What heads are you using? I see no possible scenario where that valley pan would work on a factory cylinder head. A typical “906” or “452” head does not have a continuous surface to seal to. That style pan would need a continuous surface to work with.
I would replace your pan with the same thing you have, and just vent the crankcase better.
The one thing that you mentioned, about carb spray/ intake leaks... The intake needs to come off. Make sure that the intake fits the heads correctly. You may be blowing boost into the crankcase at the intake / head surface.