Robert Mary was a famous French rider of the 1950's, from Perpignan. He raced road bikes but also motocross. In 1957 he visited Spain to try out a new model of the local brand Sanglas especially designed for motocross. When the journalist asked him what kind of bike he rode in France in motorcross races, he said he rode a Royal Enfield. Unfortunately I could not find any additional information on himl.