No early A body had dual exhaust from the factory, single exhaust was all you could get, although the "Commando" exhaust was a little better than the 2bbl version! The headpipe of 4bbl cars both came down to the "collector", whereas on the 2bbl unit the passenger side pipe died into the drivers side near the downturn!! The resonator also offered better flow than the 2bbl muffler design!