Manbearpig

There is a benelli semi auto shotgun that I am trying to get some information on. It has a serial number 121m1. I think it is a early benelli m1 variant which was imported from Italy. I think it was a Italian military shotgun from the 80's as it is inertia driven and chambered for only 2 3/4". It has a wood stock and forend and has a post front sight and a rear sight that is a cross between a ghost ring and a iron sight. I was trying to figure out what parts/barrels would be interchangeable with this gun. Any info would be helpfull. Thanks. .