I just picked this up--owner said it was all original and never polished. No swiss made marking on the dial--no zenith marked on the case--no zenith marked on the crown. I believe it must have been produced in Besancon. Let me know what you think. It seems to be running well.

 

Take a look at http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&&2uswk you might see your movement here.

 

Mine says Hello

 

Probably Besancon and not a Zenith case. Not all crowns signed from this period. Looks like the 40T movement. Chronometer grade. Look under the balance. It would be stamped there

 

The crown is not legit.
The case s/n is ordinary for gold cases made in Le Locle.
Caliber 40.
BTW look at my Zenith that is similar to yours https://omegaforums.net/threads/please-post-your-vintage-zenith.11291/page-19#post-884282

 

It’s from a circa 1950 Zenith catalog I have