In 1963 he formed his most successful partnership with the Swiss Fritz Pfenninger and they had 19 victories until 1967, when Post joined the Belgian Patrick Sercu, with whom he had 14 victories up to 1971 and his final and 65th six-day in Frankfurt.
I 1963 dannede han sit mest succesfulde partnerskab med schweizeren Fritz Pfenninger og de fik 19 sejre indtil 1967, hvor Post sluttede sig til belgieren Patrick Sercu, med hvem han fik 14 sejre op frem til 1971 og hans 65. og sidste seksdagsløbssejr i Frankfurt.