Thanks Foo2rama. The face was swapped inadvertantly by the watchmaker who didn't compare the two faces before doing the job.
The issue I have is that the case number is 166.002 but omega are saying that the old face wasn't shipped with that watch from the factory. I've done some googling and it seems that some of the 166.001 series watches did come with my old face see: (
https://www.poshtime.com/499.037/Omega-Seamaster-166.001-Automatic-c.1963.php) but there are numerous examples of that series with the new face on them too. So I'm really none the wiser about how to track down the face that I want because the case number doesn't have a one-to-one relationship with a face - rather it seems that there is a none-to-many relationship between case numbers and faces (is that true???).
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