Yep, Wendax is right, that is the story. The cars had lots of adaptions for the the Swiss roads (brakes, steering, cooling etc). On the radiator they also were labeled as such. Packard cooperated, though a regular US chassis always remained available.
Though there are indications that Graber often supplied (parts of) the body, they were not labled as such, probably because Risch was a tough negotiator and wanted to guard his specific indentity, but also because Graber wanted to be able to supply Packard chassis with bodies of his own design.