Found a 1980 Nishiki Sport on Craigslist, offered @ $75.00. Drove to San Bernardino yesterday to look at it. Something of a basket case cosmetically, the bottom bracket and handlebars nevertheless moved smoothly and silently. I offered him $60. He took it. (Yes, go ahead and tell me; I could have been patient and bought the same bike for $20 at a local garage sale. You're right, but I'm not a bargain hunter.)
Anyway, it's home now and I've got all the pieces off. Some interesting bits: (1) the manufacturer information ("G1080") is stamped on the rear horizontal dropout rather than on the underside of the bottom bracket; (2) the derailleur hanger is a separate piece that clamps to the dropout along with the derailleur.
I now want to get the frame painted as I assess all of the pieces I've removed, cleaning or replacing as necessary. Hopefully I can find a local shop that can strip the paint off the old frame and repaint it professionally at a fair price.