The lack of helical ridges in the steering column confirms a tretubi frame where only the three main tubes are Columbus SL. Given the era, the forks and stays are probably Columbus Aelle. Correct seat post diameter for SL main tubes is 27.2mm, though at 58cm it is borderline for the heavier gauge SP, which uses a 27.0mm post. However, most manufacturers ream an SP tube to 27.2mm so they only have to use a single post size, so it is usually hard to tell the tubeset unless it's stated on the decal. A 27.0mm or 27.2mm post could indicate either SL or SP.

Regardless of the bottom bracket width, I'm still convinced it is an Italian frame on the basis of the serial number format. Also, based on the serial number, it should be a 1984 model.

Both the Campione d'Italia and Nuvo Racing models used tretubi frames in 1984. Assuming the crankarms are original, the Campione is the more likely candidate. It used a Campagnolo Gran Sport group with Nuovo Record derailleurs and cost $790 US.