The Columbus decal is definitely incorrect for the frame. It's the post 1987 style while the frame is circa 1973-1977 based on the long dropouts without the spring hole. It's also an SLX/SPX or TSX decal, as opposed to SL, neither of which were available in the mid-1970s. The frame itself is likely SL based on the size and Campagnolo dropouts. However, to be sure, you should verify the seat post diameter and presence of a Columbus steerer tube on the fork.

I strongly suspect that many of fittings, such as the shift lever bosses, top tube cable tunnels and water bottle bosses are later additions.