Conn horns with the "N" prefix were created in Nogales, Mexico and are known as "Mexiconns." It is highly likely that the horn your looking at is one of these horns.Only Conn Pro-horns were produced in the United Stated during that time. One serial number chart lists 1950-1959 serial number range as being: 337,250-779657. Horns with the N prefix came around 1970, and did not follow the same numbering order.
Some of these horns play ok, but its unlikely to be an excellent horn or even good horn. They are often the same design as the "Conn Shooting Star" horns made in the USA, but often with shoddy workmanship, thinner metal, etc.
If your Vito is in good mechanical condition, it is a better horn (IMO).