I found this on eBay and couldn’t resist the guilloche dial and the 9K case. It is 32mm w/o Crown and 16mm lug width. Yes, it is a Cal. 420 from 1957, but that five figure case no. doesn’t tell me much.

Can anyone help with determining the reference?

 

Looks like an AU produced case and not SWISS so there will be no corresponding Omega reference.

 

Thanks @X350 XJR, it makes sense, and the watch is also from an australian seller. But the dial + movement combo must have a swiss made counterpart, I would think?

 

Nope

 

Who made the dial, then? The aussie casemaker?

 

Typically movements were shipped raw and the finishing components were made locally, case, dial, hands etc. Since its not a SWISS case, its unlikely it is a SWISS dial.

 

It might be a Swiss dial, but yup.

 

Thanks a lot. I have to read up on the foreign production. In fact, the dial has the standard “swiss made” print, you are just barely able to spot it.