PE, ahhh... I vaguely recalled some older technical papers on Tone Reproduction where the "World's Fair print" was referenced.
In fact, one is by Bartleson and Breneman (1967), "Brightness Reproduction...". And they speak of the 1964-65 World's Fair, prints displayed "on the tower of the Eastman Kodak Company's pavillion...".
Yes, Jim and Ed wrote an article about it and I believe that many people thought it was a large transparency. It seems that illuminating a print with a high light level can make it appear backlit and as stunning as a transparency.
We had that demonstrated in a classroom theater at Kodak.