Another often over-looked [less $$] option is to use a carb spacer. They come in either open or closed configuration and different thicknesses & materials. Of course you'd still have to determine how thick the spacer can be based on hood clearance. Typically clay or play-dough is placed on the air cleaner, the hood is closed and then the re-modeled clay is measured.
I also have a 400 and had my factory manifold notched [center divider removed] to get more mid and high rpm power. It looks stock from the outside. This is a common design feature of performance manifolds.
