You can ignore those charts for this watch. I think this is either a factory replacement case or some other type of "national production" model. There were many countries in which the local Omega distributors used their own reference numbers for certain lower end watches. It is odd, in that we generally don't see non-Swiss made steel cases on Omegas, but I suppose anything is possible.
Since the watch is in Australia, could it be that there were protectionist customs laws there in the 1950's that would have made it more profitable for cases to be locally produced? This was true in the US and UK at that time, particularly with gold watch cases.
I have to go on the assumption that the case is real and Omega sanctioned, as I just wouldn't see the point of counterfeiting a steel case like that for a watch of relatively little value.
If this were a high value Seamaster 300 or Speedmaster, I'd say stay away. For this watch, if the price stays under $300, it might be worth it because of the original dial.
Hope this helps,
gatorcpa
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