Try this link and see if there's anything useful.
http://www.yamaha-triples.org/forums/thread-view.asp?tid=4379&mid=32904#M32904
I sold my '79 750 Special a couple of years ago, but still like to lurk on the yamaha-triples.org site; it is a really solid group.
My bike used the Mik II's so I can't answer your question about the Hitachis, but I bet someone there can.