Winchester model 12 trainer, skeet or parts of parts?

I have a oddball model 12 military that I thought was and still might be a pieced together unit. It has front and rear sights. The rear sights are two pins about 3/8ths inch apart and the front is a ramp with a bb on it. The receiver is a very crudely machined model 12 marked U.S. with the flaming bomb on the right side. The safety 'off' button is odd shaped and about twice the size as the 'on' side. It has the take down barrel but where the corn cob attaches to the barrel reminds me of a model 25 set up. It has a sling mount on the buttstock.
A now deceased vet once told me that he thought it was an aerial training gun. He remembered driving a truck with men riding in the back of shooting at clays that were launched off a train car that they were driving along side of. They would have to shoot while bouncing along to try to simulate the real thing.
Any help in determining if this is an original or not would be much appreciated.
If this is the real deal I want to loan it to the local Airforce museum.

Pics would be helpful in determining anything about this gun. With military shotguns especially, it's hard to tell anything without looking at it.

It started life as a factory parked trench gun (serial number would confirm that),
In the 1950's Kleins Sporting Goods in Chicago took a bunch of surplus M12 trench guns that nobody wanted and "converted" them to sporting guns by installing longer barrels. The "mod 25" looking arrange is typical of their work.