Help identifying this c1946 cal 28.10 gold Omega

Hello people,
A non-watch collecting friend asked me for assistance in identifying this gold Omega wristwatch he recently purchased. Not being an Omega expert, all I could tell him is that:
* The movement number dates the watch to circa 1946
* The caliber is a 28.10
* Both of these imply that this watch is some manner of relative to the Centenary -- but whether the relationship is of a father, brother, cousin, uncle or whatever, I cannot say
I'm therefore posting to this forum of wise men in the hope that someone/s can help shed some light on this watch model and how (it at all) it is related to the Centenary.
Two items of note are that the bars are fixed, ie not sprung (which I find somewhat strange and I wonder if this is original to the watch), and that the caseback is not marked with a case number or Omega logo (ditto).
Thanks in advance!
David

Thanks, JimInOz.
Here's a close-up of the gold hallmark. I've also attached the highest-res image I have of the inside of the case back. If you need a better image I can ask the owner to send one to me.
Note that there are no stamped marks whatsoever on the inside of the case back, only a few scratched codes (probably made by a watchmaker or watchmakers; my guess is that if a the goldsmith made the case back he would have stamped it with his maker's mark and not scratched a code).
The watch is currently in Israel.
Thanks again and I await further input from you or from anyone else on this forum.
Cheers!

Thanks, cristos71. I know.
Can anyone here provide more information about the watch itself?
Thanks in advance.

Thank you X350-XJR and Syrte.
If anyone else would like to provide their input about this watch, feel free to do so...
Thanks in advance.

Thanks, JimInOz. I ordered an Extract from Omega for my (extremely early) Connie so I know how that works. I'll suggest it to my friend, should the information already provided here not be sufficient for him.
Kudos to you and to everyone else here who helped. 😀