"In 1956, John Edgar was waiting for delivery of his 410S Ferrari, which Shelby was to drive.  Chinetti had sold the car to Edgar, and to accommodate him while he waited, Chinetti leased a couple of cars to Edgar for Shel to drive.  One was the 500 TR that Shelby used to win Brynfan Tyddyn (McAfee was second in Edgar's 550 Porsche).  Another was the Ferrari 375 GP car pictured on your site. 

Shelby drove this car to victory in three hill climbs in 1956.  First was Mt. Washington, held on 15 July.  The following Friday, Shel won at Giant's Despair.  The next day he won Brynfan Tyddyn in the 500 TR.  Then on 5 August he used the 375 GP to win the Breakneck Hillclimb.   The GP car, as you mention, is one of the four that attempted to qualify for Indy in 1952.  It is the Ascari car, the only one that qualified.  Note that the body had been modified since the car ran at Indy. The car's original serial number was simply No 1.  That was changed to 0388, in Ferrari's normal sports car numbering series, probably when the bodywork was modified."

Photographer Earl Gandel offered an interesting anecdote:

"One other fact about the Ferrari; a technical fix made to keep the rears on the ground during acceleration at the hill climb was a lead weight, wired into the tail of the car after a ragged hole was cut in the metal.  Ah, '50's technology."