Hi,
I bought a kit some years back and have started using it for many of my 350/4 and 400/4 parts.
I fully agree with the earlier replies that the finish you start with on your component reflects the finish you will achieve after plating. Rough, pitted parts can still be done if cosmesis is not critical (parts you cannot easily see) but they will at least be protected.
Mine is a Gateros kit and I have no connection with that company but am pleased with it. I am fortunate that I have a stabilised power supply, with variable current and voltage - which makes for repeatable results.
I put a page on my web site about this topic and it appeared in Tansha a while back.
http://www.stallard-engineering.co.uk/stories/Bikes/Japanese/Zinc%20Plating.htmRegards,
Ian