Garry,
you are close, it isn't the Pininfarina but one of the mock-up models that were made for the Daimler board to look at and decide which one they wanted. Luckily, as we all know, Barenyi's Pagoda roof won out. All the different models for the board had the gangsta-style whitewalls but they are rarely seen in later company photos.
The car at the Geneva car show where the new W113 was introduced already had the Continental tires with the narrower band similar to the one at the US introduction shown in this photo: