Do not let the components fool you, really often I have found that parts from prior years get hung on later built bikes, just in time inventory was not a production mantra back then. Parts if stored well did not "go bad" and were not redesigned as often. Tires even improved with ageing. I would go by the finish first, serial number in this case too, components last. Looks to me that there might be a Campagnolo sport spring hole above the rear mechanism mount hole. so that pushes it more to your date.