I've attached photos of my AE two barrel set, which letters out as a 30" single barrel gun (a Roe Clark letter from maybe 10 years ago).
Taking a look at the pics of the barrels/forends, it becomes immediate clear that the 26" barrel set was added after 1911, as the forend iron has the 1911 patent date.
Because of several factors, I've always believed the factory fitted the 2nd set of barrels, and would be interested in opinions.
I originally bought the set as a project, thinking that it would be an ideal project due to the two barrel sets. But, that was a long time ago and as I'm simply not involved in hunting, I have a feeling that the project will never take off. The gun is devoid of original finish, but the frame and related pieces are also devoid of any pitting or such, which suggested to me it would be an idea candidate. Best laid plans.....