ChiefShotguns,
Oh yeah ...Elmer Miller did have a selector like that in his model 11, which I thought that model was a SxS design...I looked at the 1929 O/U trigger because it fit with your date code of 1933...there's probably several plausable explanations as to why a post 1939 trigger would be found in a 1933 proved gun...I'll keep checking and let you know what turns up. The more I learn about the history of single triggers, the more I realize the importance of Millers role over the decades.