Gents,
These brackets/plinths are definitely handed and the French ones are equally definitely not the same as the Slough parts. There are two main differences ……
1) As Patrick says, the profile of the domed top (to match the recess in the lamp) is not the same for the French (Marchal/Ducellier) headlamps as the English (Lucas) version.
2) In addition, apart from the very earliest versions, the French parts have a slot to access the lamp fixing nut. This is clearly visible in David’s pictures above. Slough parts never had that slot.
I may have possibly have one in my stock. I shall check when I get into the garage later this week.
B……………