Any importer's markings? That might narrow down the model some; there were several who had versions of the San Uberto made specifically for the American market with single triggers, pistol grips, and small beavertail forends.
Or it might have been ordered with these special features for an American customer. Back in the 1970s, I ordered several Bernardellis with specific features that were not found on any stock model (to be clear, they were standard features on some models, just not the ones I ordered them on; they let you "mix and match" features on a gun you ordered specially). This could be done through any FFL dealer at that time and I'm sure that many "non-stock" guns were so imported.
