The fact that the map shows okapi in the old Deer and Cattle Sheds indicates that it could not be after 1952.
The building labelled African Elephant on this map is the old Tapir House which, as I mentioned in an earlier post in this thread, was sometimes used for elephant accommodation.
African and Asiatic elephants were definitely kept together before 1960; I can recall seeing them together in the enclosure shown in this picture during the 1950s and this is mentioned in guidebooks from this period.
A quote from the 1954 guide (the same text also appears in other guides from the era):-
“Their dens are underground, and they are approached by a ramp leading down to them in the far corner.........At the western end there is a small pond and the smaller elephants enjoy a bath here during hot weather”