Hey
Krusty, you beat me to it and worked it out yourself...good on ya!
Well your machine is a Series 1, solid engine deck 17" Model 45 machine, with the Kirby Lauson (Tecumseh) engine, manufactured in the Scott Bonnar factory in Thebarton South Australia. That model was first introduced in 1968 and manufactured until the introduction of the twin rail deck design in late 1974 early 1975.
With the Kirby engine, we cannot establish a date of manufacture, and hence cannot accurately date your machine.
