Jacques Anquetil used a plastic Simplex Prestige rear mech in the later stages of the 1962 Tour de France. He went on to win the 1962 TdeF as well as the Grand Prix des Nations that year using this gear. Other notable 1962 victories using the gear were Jean Stablinski in the World Championship. I believe this model Prestige was the 532. They were widely on sale in the United Kingdom in early 1963 and probably before. Much to dear for us schoolboys then, had to make do with Benelux Mark 7's.
Best wishes and be lucky. Michael Butler Huntingdon UK.