340 intake/carburetor advice

If your going ahead and reaching for the 3.91 or 4.10 gears, then I’d definitely be going with the AirGap and the 800 cfm AVS2. You won’t have the outright “full blast” performance that you would with a double pumper carb, but you would be very close and have very good street manners. No other manifold will match the power output with a street oriented cam.