It is a calibre 265, and is identified by the number under the omega emblem beside the crown wheel. The longer number beside the ratchet wheel is a serial number that is unique to the movement and can be used to work out the rough date of production. Omega maintains a vintage database that gives the model reference and correct combination of calibres and cases, as well as other information. It's not compete though, so failing to find a watch there doesn't automatically mean it's a fake or Franken.
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