Panhard Dyna Junior by Pichon & Parat / Vivez c '54 ?
It is a Panhard Dyna, yes, but the builder is actually unknown.
I only know of one picture of this car on the 'Net, which is on a well-known French site where the poster says he long thought it was built by an obscure coachbuilder near Bordeaux, but a Panhardiste has now told him this is not correct and it still isn't known who built it.
The car has survived but is in a very sorry state somewhere..
I think we'll call it solved because we're never going to find out who built it!