The Rootes Australia factory was located at the southern end of Salmon Street.
(The current GM Holden factory is at the northern end, on both sides of Salmon Street).

It was bounded by : Plummer Street to the north Prohasky Street to the west Williamstown Road to the south Salmon Street to the east

Here are two pictures at the Sunbeam Club website.
The first one ("most likely taken in the late fifties") is looking to the west.
Running left to right:  Salmon Street in the foreground, Prohasky Street in the background.

The second photo ("taken a few years earlier") is looking to the south west.
It is centred on the eastern half of the complex.  Clearly visible in the background (top-centre) is Leith Crescent, so you can follow the line of Smith Street northward from there.

Google Earth users:  Click here to run a placemark tour of the area.
You will need to occasionally pause during the first time you run it.