Bill,

the town of Ovens still exists and is not far from where my grandfather and other relatives live near Myrtleford.

https://en.wikipedia.org/wiki/Ovens_River

Its not really on the route between Melbourne and Beechworth though. I think perhaps he is using Ovens/Ovens District in the sense of the areas that the Ovens River flows through or even the general Ovens Valley. In which case yes Greta would definitely be in the Ovens valley.

https://en.wikipedia.org/wiki/Ovens_River

Its a beautiful part f the world.