THIS IS THE ONLY MANIFOLD FOR GMC MOTORHOME WITH A 455.CUSTOM MACHINED TO FIT THE CARBURATOR .Custom trimed for GMC motorhome with 455.Has the AC bracket mounting surface machined, hole drilled & taped. Has the intake chamfered to clear the secondary throttle plates. With out these modifications one will not be able to use the manifold as is. Built-in exhaust bypass. Identical fit to original.GM08-006-27.1 It is highly recommended to use the intake manifold gasket kit with the sealant. You will need to use electric choke and special pigtail connector.