I think this was built by the Federal government back in the day. It was the primary gateway to Australia. I think most Australians and visitors arrived and departed form Sydney International Airport with interstate connections (mainly propeller aircraft) from all sates and the two territory's here in Australia when this international terminal opened. This terminal was built to accommodate the future 747 mass transport arrivals and departures.
Fast forward forty nine years later to October 2019 and Qantas has just six 747-400's left and Thai Airways still use 747-400's to Sydney too. A380's, A350's A330's & 777's 787's now park in their place. Same International terminal by the Cooks river with fuel depot and freight terminal in front of that to the top right of the original picture above shot. (where the Norfolk Island trees are in the first shot next to the building by the Cooks river) A multi level long term storage car park that will cost you more than your entire holiday is directly behind the original terminal. Look very hard and you will see the original terminal