Hi Mike
I agree that there is a lot more about the French available in French, but limited sources in English without looking at primary sources, as you have done.
Maybe I should have specified the mounting for the racks, rather than the racks themselves !
Certainly when adding mounts for cameras a lot of work was carried out at the ADs as this was more practical than dealing with the manufacturers or doing it on the squadrons. See, for instance, the recent back page of the Journal images of the camera fitting on the Morane parasol.
Nick