I finally got my "wall hanger" out of lay away. It turns out the A&N gun has London proofs and not Birmingham, that's what has been throwing me. On the flats is the 12 with a C below it in the diamond so it appears to have been proofed prior to 1925 indicating an original chamber exceeding 2 1/2". So the barrels are still in proof. The screws I thought to be stripped are not. My $200 "wall Hanger" is looking like a gun with some potential.