blomman Mr Blue
38586
Welcome here!
The caliber 343 (if I am not misinformed) existed both as Chronometre and non-chronometre.
As for the crown, yes it is replaced.
Please post some better photos of your dial and inside of the case back + movement.
Maybe we can find some more info on your watch...
Here is a scan from a 1958 Swedish Omega catalog showing a similar watch as yours without the Chronometre...
Hope this helps.
Best
Blomman