[CR] MAFAC 'Racer' variation info sought

I recently acquired a set of Mafac 'Racer' brakes in a lot with this unusual top mount for the rear brake bridge. See link to photo:

http://s517.photobucket.com/albums/u335/gypsybike/RESEARCH%20MATERIALS/?action=view&current=000mafbr2.jpg

Anyone have information on this? Is it rare? What brands used this on their bikes? I was never aware of it. I checked, a standard mounting bolt and spacers can be substituted for it.

Jay Dubiel
Halifax, VA USA