A 12 speed most likely points to 1984--- unless someone in the past upgraded the original 5 speed freewheel on a 1974 to a 6 speed Ultra or narrow spaced Suntour, Atom or Regina. However, with that said, IIRC, the four digit date code stamped in head badge did not become universal until 1975-76? My money is on 1984. Take a look here at this
Findley-Cooper Page.