crosswind air gap or stock 4bbl manifold

You don't mention valve size which would indicate what the bowl and transition might look like but you may already have too much port valume. That makes it sluggish even with a smaller cam. I would keep the setup you have, or locate a 318/360 Performer to use on it and don't port match it to the 340/360 but maks ure the roof of the intake and roof of the head port opening are matched in height (you can leave the intake's port narrower). That smaller intake port will help the response a little. If you run the larger cam I'd expect it to be flat regardless of whatever you do.