After seeing the original post and pics . I finally went and dug out of my safe a similar shotgun.

Here are the stats.
Winchester Model 12 S/N 92637X
Barrel length 20 in.
Barrel marked cyl.
Barrel date 41
Large Ord. Bomb on top (like on early 97's)
Receiver/barrel ext. match
I can see no markings on the stock (probably a old replacement)

I purchased it about two years ago off Gunbroker for the price of a common model 12 riot.

I am glad to see similar marked shotguns
Maybe more will come to light.

John Ed