Brought out in 1979 as the z500b1 in black or silver, it met with little success to combat this Kawasaki sanctioned a 500 race series, basically standard bikes with few modifications were allowed.
My own z500b1 is a raced example! It was updated in 1980 as the z500b2, but again sales were slow. It was later replaced by a whole series of 550's (z550, zx550, gpz550) and its final incarnation was the gpz600.
I have very little information about the z500 so if you have any details pass them on!