My sympathy.
If it has a steel back, it cannot be 18k solid gold. Plated like you said would not have much value. In case of solid gold, its weight would be around 30g so its worth would be that of the gold content plus about $500.
In the Omega vintage world, all the ID info is inside the watch and it's close to impossible to identify the exact model by just looking at the outside. It's definitely pointless trying to ID through a similar watch.
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