Thanks!
I called the Biscaretti Museum today, but all cars are in storage and my English and their Italian couldn't communicate.
There were about 40 coachbuilders in Levallois-Perret, so far I researched about 25. Problem is I don't have the complete list, so I'll need some more help - unless someone else finds it first. So a lame question, does the first letter of the name of the coachbuilder is in the A-L range?