At the end of 1963, the serial #1962001 was assigned. From 1964 - 1966 a clean up of production took place. Ending serial number was 1970875. In 1972 the Y model production began. All of these guns came out of the custom shop. None of them used leftover parts. My information indicates that Serial number 19671xx was part of the "clean up" production that occured between '64 and '66.