Re:
Yes, the steel and aluminium frames built in Taiwan have a two digit year number after the first letter that signifies the factory (H = Hodaka, F = Farley).
The other Hand Made In U.S.A. steel and aluminium frames have various prefix letters depending who manufactured them (Altitude, Enigma etc.)
The year of this Hei Hei may be determined by the decals (if original), the cable routing and the slope (or not) of the Top Tube.
Pip.