Strange Omega - Please help .... !!

Some time ago I inherited a watch from my father.
And my father got it from his father (from my grandfather).

Unfortunately - until today I cannot identify him.
I searched on the internet but I can't find the same ...

All I know is that:
- there is a gold mark on the envelope,
- my grandfather could buy it in the period (around) from 1920 - 1980.
- was bought used (not new)
- he bought it in Luxsemburg, France or Switzerland (he stayed in these three countries)

If anyone knows what watch it is, please let me know.
Thank you in advance for your help.

Pictures are attached.

@ JimInOz

Thank you for Your answer.
From this it follows - that I need to find a good watchmaker who should open the watch and take pictures.
As soon as that happens, I will post them (pictures) on this forum.

thx