I just checked if my v. old pair of Berthets were suitable for a 1938 bike, and lo and behold, they are listed in the 1939 Brown Brothers catalogue, be it with different dust caps from mine, but that´s just the way it is, I suppose. I hope my karma rating won´t fall below a bearable level if I fit them first and look for older dust caps later.
So I guess 1960s should be ok.
Toni Theilmeier, very on topic in Belm, Germany.