Datsun 1200 used different Hitachi alternators over the years. Starting with the LT-135 small diameter unit. circa 1974 started using the larger diameter LT-150. In 1981 started using the built-in regulator LR-135
Identification: LT135 has a black plastic grille on the back
The larger ones (LT150) have no black things on the back. Just the metal case