The only French I know is Chevrolet Corvette Coupe, but my XK120 FHC was originally sold to a French nightclub performer named Robert Lamouret who lived in Paris, and presumably it wore French license plates before it came to the US, so perhaps I can contribute something useful to this discussion.
Leaving out the alloy cars and only considering the steel cars, there are two different rear panels suitable for USA size plates, and two different panels suitable for European size plates. There are differences, not only in the obvious bolt pattern for attaching the license plate, but also the bolt pattern for attaching the panel to the boot lid. Mine was changed from the Euro size to the US size in the 1950s or 60s, but with the other panel attachment pattern, so I now have 8 holes in my boot lid.
