CALIFORNIA DREAMING The proverbial sports car pantheon is full of models that have achieved one kind of metric or another, but at the very peak of Olympus two words loom larger than most any other—California Spider.

Ferrari had achieved great heights with its 250 GT platform ever since the FIA changed displacement limitations following the disastrous 1955 24 Hours of Le Mans, finding remarkable success in sports car competition with models such as the Tour de France and Testa Rossa.

Alongside these wondrous racing machines, Maranello built a magnificent line-up of roadgoing 250 GT coupes and cabriolets that came to define the peak of engineering and style.

In 1957, however, one man dared to push the boundaries even further.

John von Neumann was a California-based importer and co-founder of the local sports car club who had become a regular distributor for Ferrari sales on the West Coast.

He proposed the idea of a dual-use open Ferrari that could be driven to the track and raced be...