Agambard, the tube diameter on the Model 1918 is 7/8" (from memory) not 1" as per the Aldis, so it will not fit in standard 1" rings, unless sleeved.
Sam, the scope is definitely an Aussie produced example, not Brit. Even if most of the original markings are now lost, the fact that it says 'Sight Telescopic' makes it AOC as the WW1 PPCo produced examples were not so marked. As regards worth I have not sold one recently & am in the UKanyway, so I would not like to hazard a guess. As you are in Oz it might be better so solicit an idea of value from other knowledgeable fellow countrymen.