He probably intended to call it Once upon a Time the Revolution, but then it was called Keep Your Head Down (Giu la testa).
Duck you Sucker is bad, but was Leone’s choice for the English market, and A Fistful of Dynamite shows only the helplessness of the English distributor.
I think Giu la testa is the best title as the better sounding Once upon a time title does not really fit the film.