There was no point in keeping this puzzle alive. According to Paul Schilperoord who wrote the book on Josef Ganz and who has most of the original photos from Motor-Kritik there was a picture where the name of the coachbuilder was clearly visible.
My only problem now is the original Motor Kritik article which alludes the design to Richard and Xaver Küchen. They designed motorcycles, including the K.
This car was supposedly built on the basis of a Zündapp "lieferwagen" (small transport vehicle). According to Paul, Prototyp Museum has the chassis - so I'll contact them. For now it is merged.
