I still believe, that this car is the Porsche Ghia prototype from 1960 (rear-engined 4-door sedan). As several times to be found in several publications (printed and online).
Type 764 isn't listed as a 'Prototyp', but 'Studie', whatever that means. I believe that the prototype is a driveable car, 'Studie' could also be only a sketch....