Is this 1955 Triumph Trophy James Dean's motorcycle?

I tend to associate James Dean with a certain Porsche 550 Spyder, and Steve McQueen with Triumph motorcycles. But James Dean was apparently a Triumph rider too, and the bike he rode was a 1955 Trophy. The shots were sent in by Andy Enness, an Australian now living in New York. Enness works with the legendary Hollywood photographer Phil Stern: “One day I was over at his house in Los Angeles and stumbled upon an old pile of photos of this Triumph scrambler.' 'I quizzed Phil on them and was told how James Dean’s brother had asked Phil if he...