Based on the CdM decal it is post 1974, while the lack of Portacatena dropouts suggests pre-1978. I can't make out the 2nd character in the serial number but it appears to be a 5, in which case it is a 1975-1976.

The components are not necessarily a reliable indicator of the model, as some have obviously been replaced. This could be Specialissima or a lower racing model like a Speciale or Rekord variant. The best indicators of the level of the frame is to determine the grade of the tubeset. This is achieved by determining the diameter of the seat post ( often stamped on it) and checking inside the bottom of the fork's steerer tube for the presence of Columbus' patented spiral ridges (see pic).