If working on the carbs does not fix it look at removing the intake manifold and valley pan to see if the intake to the head fitment is good or wobbly
I take a feeler gauge and try shoving the thinnest to the thickest ones I can get to slide under the intake to the head on all four corners, top and bottom edges and write those number on each corner to see if there is a pattern or so the machine shop can machine the intake surface so it will sit flat on the heads
I do ask for a tiny bit(.001 to .0025) tighter, tapered, on the bottom sides than on the top so it will pinch the bottom tight against the heads and intake manifold I do have them cut a little bit more(.015 to .030) so I can use the thin fiber intake gaskets on the head side minimum, it doesn't hurt to use them on both sides of the valley pan if needed