I remember that my first Nishiki (a Custom, c. 1971) had Shimano Eagle derailleurs. The Custom was hi-tensile, nothing special, and pretty heavy. The Eagle derailleurs were low-end, match the frame pretty well.
I don't remember the GTO designation, and wonder if I've simply forgotten that or if it was an improved version of the Eagle. But it does seem to me that part of the Eagle was drilled somehow: there was so much metal in those things, especially something which appears in my minds as a guard of sorts along the bottom of the derailleur, that drilling wouldn't have weakened a thing. It certainly would have made it look spiffier than it really was.
I don't remember my Nishiki having Shimano cranks, Eagle or otherwise. I'm pretty sure the cranks were cottered, though.
In contrast, my next Nishiki, a Competition, was Cro-Moly with SunTour VGT derailleurs and barcons, and a really nice Sugino Mighty crank (the Campy copy).
If you get to see the Schwinn and the Eagle GTO components in question, Marty, I'd sure be interested in hearing more details!
Spring Green, WI