Correct barrel for 1915 2 3/4 HP

[lindsay@melb]

I am trying to confirm what the correct fin pattern is for a 1915 2 3/4 HP barrel. When I look at photos of motorcycles I see different fin patterns and have also seen different styles fitted on the front and rear cylinders of the same bike. I assume that the fins should be the same on the front and rear and expect that people have compromised and used the best pair of barrels that they find. Can anyone confirm if either the two barrels on the left of the picture below or the single barrel on the right hand side are from a 1915 Douglas? If not what year of bikes do the barrels belong to? Your assistance is appreciated. Lindsay.