Ah the YZ80J. I never did get myself one of them as I was too old and too big. But I did have the YZ125J and I did get hosed off by some fast kids at a club day at Connondale on their YZ 80s. From memory that could have been Tam and Ben Paul.
Funnily enough, if you look around and talk to people, there must have been millions of then made as so many people owned one or more over the years. They are so legendary that you often see YZ80s from the mid 70s to the late 80s advertised as YZ80Js.
I guess they had their faults, buy how popular were they back then! Enjoy the project.
Retro