Originally Posted by cyclotoine
T-mar doesn't seem to be as active on the forum lately...
... but you could always PM him. Based on my current understanding of the Nishiki serial numbers, I would place this frame as 1979-1980. The 1978 model used SunTour/Sugino/Dia-Compe. I have nothing on 1979-1980. The 1981 did use 600EX. It was back to SunTour/Sugino/Dia-Compe in 1982. So everything does point to 1979-1981. Date coding the 600EX components, as suggested by Cyclotoine, should help to narrow things down. As John E. states, the Cmapgnolo parts are aftermarket upgrades.
Sorry I haven't been around as much lately. Spare time has been at a premium. I'm technical advisor for our local sanctioned race which is this weekend. My presence should increase starting next week.