KK, all good, will go with OEM’s. I think the same bushes were used on other Kawasaki road bikes of the time, particularly the triple two strokes. I think cast iron was used because it is probably cheaper than brass and was a common bearing material as it can be used with a hardened steel shaft due to the coefficient of friction being relatively low, cast iron having 2 to 4% carbon. The cast iron glazes over therefore wear becomes negligible. However it is prone to rusting and hence the drama getting them out if stuck to the hardened steel sleeve.
I had interpreted the label on my NOS bush as having the ‘Big K’ logo and lower case company name, as being a 1980’s style used from 1980 to 1989 – a 1979 label would not have had the logo and KAWASAKI would have been in upper case (type 3 in John Brookes book). Cheers