I don't know much enough about vintage JLC pieces so I will refrain from commenting too much. It is a sweet, beautiful, vintage-looking and symmetrical watch to my eyes. But I will have hesitation wearing it while submerged for the fear of accidental pressing on the pushers which in this case will most likely allow water in.
I assume there is no continuous seconds on this watch, correct? Watch will look perfectly still if the chronograph is not activated. Not that there is anything wrong with that. Just an observation.
All in all this is a fine piece by my book. But I think it should be meant more for collecting/casual wear than serious submersion.
Where this place is I don't think I can guess with any accuracy. But let's try the underground of Canal St. Martin? It's the only place I can think of from past literature and photographs I have seen.
Ruckdee