Interesting. As many know, I personally prefer to retain the original 6V system for non-Slough cars but I have looked at the information on this website and it does certainly seem to be a practical solution for owners who do wish to make the change to 12V.
As Alain says, this method is only suited to post ’52 vehicles (wipers mounted below the screen) but there is further information fr a 12>6V converter suitable for earlier wiper motors and other devices.
There is also a lot of additional information pertaining to a 12V conversion and a link to a source for a suitable 12V (and also 6V) alternators.
All the information is available in downloadable PDF documents (in French).
B…….