Agree with Don, a rather 'rare' Model 21. If used for waterfowl with Kent TM, the chokes may be ideal as the Kent patterns much tighter than the kead shot of the guns era.
One of the steller atributes of the 'Duck' is the 13&5/8" LOP. Really makes a difference when cold and wearing heavy clothes. During Graduate School. My buddy used to borrow my JC Higgins Model 20 pump i purchased as a child. He said that it was the most comfortable shotgun he had ever used for waterfowl. Turns out that when I purchased the gun at 13, I had the stock cut down for me with pad.-Dick