Update after receiving an email from Longines this morning :
"Originally, the serial number 7'467'151 identifies a mechanical Longines movement with manual winding, caliber 23M. It was invoiced on May 18, 1948 to our Longines subsidiary in France.
The other parts of the watch were manufactured locally under Longines license. Unfortunately, since we do not have the records in our possession, we are not able to give you more information about your model."
So it's a caliber 23M (congrats
@DirtyDozen12 
)
According to the email of Longines I conclude the watch is all original : all is well that ends well !!
Again, thanks a lot for your help !
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