How old is the gun? Only reason I ask is I have an old Eastern Arms Co. SxS 16 gauge from about 1921. It is Belgium made and nowhere anything like a 311 Stevens. Even if you gun is close to looking like a 311, I doubt very much the stock would fit without major modifying. A lot of times a stock on a SxS won't fit from one of the same model to the next without some work.