1913 Harley Davidson Twin Cylinders discovered

Matched serial numbered set of rough 1913 HD twin cylinders. On the back side ,at the base of the cylinders are the serial numbers ,then on the cases below one would see the same numbers, After 1914, HD ceases numbering the cylinders.One can see the exposed valve spring, one per cylinder, Starting in 1914 all engines would be fitted w valve covers, note 1 valve cover per cylinder vs the 2 valve covers in later bikes. the fins are busted off but the cylinder base corners are all intact.amazing!
No primers on the backside of the cylinders either, One would open the primer and inject fuel,my guess is that after HD experimented w "atmospheric valves" someone engineered the early primers to the cylinders to inject/deliver fuel directly into the combustion chambers for easier starting. My guess is the "fuel vacum" of the early carbs just wasn't enough to get fuel into the combustion chamber.The primers ,one per cylinder start in 1915. the cylinders on the early engines are the hardest to find, So one could use 1913 Twin cylinders on 1911 thru 1914 models only.No one as far as I know is reproducing early twin cylinders, and NO ..one cannot interchange Single cylinder barrels on Twin cylinder barrels.. next to get the rest of the engine ,...the old foto is a 1912 or 1913, cannot be a 1914 because?
No valve covers, No footboards, No 2 speed shifter on the gas tanker.