That motor is a genuine unit out of a 83/84 Z50R and with the wheels the round hole are the early J model and the others are off the R model. J's are a bit stronger because they have a 4 bolt hub compared to the R's that have only a 3 bolt hub
It i crazy fast in a stock roller. I built and fitted the motor for the guy. Cheap for what it is. The shock was one of the last ishocks made so it's the big shaft model.