I was present at both the unofficial unveiling of the Wall (Winterland, February 1974), and the official unveiling (the Cow Palace, March 1974). After the Cow Palace concert, the audience, on the way out, receievd a free 4-song single size 33 rpm sample of tunes off the forthcoming dead family albums. All this for $4! Times have changed.
My favorite factoid about the wall is that the tallest colume was 32 feet high. Why 32 feeet you may ask? Phil's bass was quadrophnic - each string had a separate pick-up, each going to its own Mac 2300 power amp. The low E string, played open, put out a wave that was 32 feet from crest to crest. The idea was to produce an entire wave, not just a part of it. The wall took so much time to set up that the Dead had to have two of them, leapfrogging each other around the country as they toured. It sounded incredible but, from what I've read, nearly bankrupted the band.
Bill, the guitar one