According to the Black Book, Rob Walker's car was chassis F2-9-58, and a Type 45. It was not at all unusual for Walker's cars to be the previous year's model.
The race at Rheims was held after the Grand Prix the same day, and it was incredibly hot. The tarmac was melting on the road, and many drivers failed to finish the race, especially those who had already driven in the GP. Moss of course wasn't like any other driver!