I had an Antonio Zoli 20 O/U back in the 1970s that sounds a bit like the one you describe. Can't remember the model name but it was a boxlock w/case colored sideplates, two triggers, extractors, a solid rib, and sling swivels. NOT a high grade gun but killed chukars like a champ.

75mm chambers, OF COURSE (never had an Italian 20 that didn't....).