Lefever serial number, different on both barrels, usually mean the gun was rebarrelled or some replacement was done later than the manufacture of the gun. This gun may have been barrelled with the original serial number, and soon after, another set of barrels was selected for final assembly and shipping. The lower number (the barrel not matching the rest of the gun) could have been the number assigned to the final replacement barrels. If the lower number had been a mistake, they would not have left it in place. I would be buying this gun for $600.