My manifold is fine other than the 2 busted bolts. Could I possibly just cap of where that valve is? Or if I could find a way to get the busted bolts out. They are very stuck.
Unless You're having fuel-vapor/boiling in the carb issues, just make sure the flap is working correctly. I believe some have made a "block-off" plate out of stainless sheet, but cold weather warm-up performance may suffer.