I'm not having much luck on your gun so far. If you can, would you check it for proof marks on the barrels near the hammers, and any other engraved lettering on the rib between them and post pics of anything you find? Everything I've found so far leads me to believe that your gun is English made, and would have been a really high quality gun in it's day. Another thing, looking at the photos, the metal looks pretty dry. It would be a very good idea to get a soft cloth with gun oil and wipe it down. That will help remove the grime, and also help preserve the metal.