One of the earliest, if not the first, US rider to ride a Yamaha, was Roxy Rockwood.
Picture received with thanks from Guy Reynolds, Yamaha US, Kennesaw, Georgia.
This "Yamaha News" 1958 issue pictures him at the start of the Riverside, California race (Sept 14th, 1958), which he finished in 3rd position.
Roxy is astride one of the famous Yamaha "PQ" racers, the Catalina race machines.
The old Yamaha magazine is signed by Roxy himself!