Beacause I have known of this engine for many years, seeing it still unidentified at Murray Bridge, then this query, I decided to ask about it on Facebook. There seems to be more activity on there than on forums such as this (sorry Michelle!).
The Sarolea answer may be correct, but I am awaiting further confirmation. Sarolea engines were usually on motorcycles, but this did not come from a bike. The cast iron construction suggests stationary.
Eric