From 1976 on Colnago used Campy's 1010B style short rear dropouts. Your frame has standard Campy long 1010A dropouts.
Also, the seat stay tops would have been fluted on 1970's frames and flat with Colnago stamped into them on frames from 1980 on.
1983 BB.
Chuck Schmidt has a good Colnago time line:
Velo-Retro
verktyg
Chas.