Since engine oil additives are designed to reduce metal friction, adding them to areas where the clutch mechanism is intervening will cause the clutch to slip and cause problems.
Honda CB 1100F should not be used because of its multi-disc wet clutch mechanism.
I looked up the specs for a 1956 Harley Davidson FLH on the internet, but I couldn't find them. If the engine oil injection point and the gear (clutch) oil injection point are separate as in current Harleys, I recommend Bell Hammer Seven. However, if the engine oil injection point and the gear (clutch) oil injection point are one piece, the clutch will slip and cause trouble, so please refrain from using it.
I am sorry that I could not give you an accurate answer.