Originally, the Transformers series in Japan is a re-dubbed version of the US series. When the series ended in the US, Toei produced a continuing series as Transformers still proved to be very popular in Japan. The final three episodes of the US series was disregarded from the Japanese Transformers continuity.
The Headmaster characters differed from the US version. The American version of the Headmasters were aliens in body armors that transformed into the heads of the robots. In this Japanese version, they were actually really small robots who could transform into the head of a larger robot.