Some time ago, I became the caretaker for an all-black but somewhat be-draggled Zunow frameset. Actually pretty conventional for a Zunow, but does have the Pentagla chainstays, and hummingbirds engraved on crown caps and seat stay eyes. And h'bird shaped BB "drain" of rather large size. 57 cm seat, ctc; 55 cm top, ctc.
It can't be earlier than 1977, since it actually has short Nuovo Record dropouts without eyelets (drilled and tapped for chain holder), which the Campy Time line http://www.velo-retro.com/tline.html puts in the Catalogue 17A supplement (thanks, Chuck!).
A question: when was this special chainholder rear drop discontinued? That would roughly bracket the age of the frame.