How strange I have no memory of it. I was a regular visit to the old Monkey House which was the forerunner of the Sobells, but this area remains a blank for me.
This old Pelican Pool was a rather uninspiring exhibit so it is not surprising that it was overlooked especially by people, like the two of you, who are obviously very interested in primates; I doubt it would have diverted your attention away from the inhabitants of the old Monkey House that was nearby.
However, it is worth pointing out that the Pelican Pool was still shown on the London Zoo map for 1970 although obviously it had disappeared by the time the Sobell Pavilions were opened a couple of years later.
It was an exhibit that showed all too clearly the limitations of the postage stamp mentality. "We must have pelicans for the public to see, now where can we put them?"
I'm not sure that they really represent the best usage of Three Island Pond, either. Personally I'd install them on the lake on the Asian Drive Though at Whipsnade.
I would be interested in seeing any photos of the Great Aviary, the neighbour of the Pelican Pool. I rather suspect that it was a better home for its inhabitants than the Snowdon Aviary.