I think your gun is a well executed copy of several English guns that were in a one or two man gunsmithing operation in pre-war Japan. There are a mix of features (the barrel rib extension, the lock screw on the lever screw, the raised metal sections near the detonators) that never seem to appear on any single model of English gun.
I would guess that the crew took some measurements, added a few refinements, and had at it, producing a boxlock. There used to be lots of one man shops in Japan, and some day I'll show you a photo of a custom 7mm magnum Remington my Dad had built when he was over in Okinawa.
My Dad had a hell of a time trying to explain to the guy that he couldn't blue the barrel-Dad finally held up his Zodiac watch band and asked the guy "can blue?" That's when the light went on in the guys head. He black chromed the barrel.
Dad said there were lots of little shops that did various levels of custom work, circa 1962. If I didn't tell you it was done in Japan, you wouldn't know.
Best,
Ted
