The thing is this is where memory begins to play tricks. Adult male gorillas are from 1.4 to 1.8 metres high and between 136 and 227 kg in weight, and they would be silverbacks. Females are noticeably smaller. Western gorillas also usually have a silvery grey wash through their hair and often have a reddish forehead. Check some photos online if you don't believe me.
A male chimpanzee can be a very impressive animal and can be as large as a female gorilla, as well as having all black skin and hair. I would think it quite possible that a large male chimp may have been separated from females and juveniles, and so by comparison seem much larger.
Having said that talking to a mate I have been told that Perth did have a Director in the '60's and '70's, Tom Spence, who was a primate nut. He used to have one of every primate species he could lay his hands on. It is possible that he had one gorilla. However my friend thinks this is extremely unlikely, if there was a gorilla everyone would have known it, and they certainly did not have them during his time in the '80's and '90's.
For myself I remember going as a child to Taronga Zoo in the late 1960's and making quite an effort to see "King Kong" as the only gorilla in Australia. In 1974 I did work experience at Melbourne Zoo and was introduced to their new juvenile pair as the only gorillas in Australia other than those at Taronga. Later in the 80's and early 90's I was involved in Melbourne Zoo's Friends, and so followed closely the development of the rainforest and the integration of the last pair from Taronga, leaving according to their publicity to Melbourne again being the only zoo in Australia with gorillas.
