Yours friend's memory sounds right. Old ads and reviews show the Guerciotti still using cable clips on the top tube as late as 1978. The decal style had changed by at least 1984. So I'd say it is 1979-1983. Hopefully, someone else can narrow things down further.

You can verify it is Columbus by checking the bottom of the fork steerer for six spiral ribs. According to the 1978 review, frames 60cm and bigger were made from SP as opposed to SL. This was a fairly common practice during the era.