I think that is the 2 1/2 gallon tank that only was made in 1943-1944, right before they went to the single side fill tanks.
Tom, I would say this guy is not a Simplex guy. In some of the auctions he says he doesn't know anything about Simplex, but got the stuff from an guy that had Harley stuff. I bet it was bought at an estate sale, if I had to guess.
Pictures saved for the future. If anyone knows more about this tank, please speak up! I will change the topic name and move it into the proper place for gas tanks in a week or two.