I just found a pretty cool book -- published by Gibson's Lustrum Press in 1978 -- that details some of his late-70's darkroom practices. And a lot of other folks' too. Title "Darkroom" edited by Eleanor Lewis. A second "Darkroom 2" was edited by Kelly Jain but *sigh* my library doesn't have it.
I'm fascinated at his mention in his Bergamn GRaphics interview about scanning WET prints -- I've been reluctant to try but might just go for it (like a wet-gate cine transfer? hmm). The Leica stuff has the most attenuated gray tones I've seen from him yet.