As an old lag (but not compared to some) in the UK racing scene - I can only observe that the most common lightweight rim in use during the late 1960s and all through the '70s was Fiamme...
In fact they were so common that familiarity bred contempt and everyone wanted something else rim-wise but few could afford an alternative. Fact is that my straight stay Hetchins sported Fiammes (36 / 36) and Barum tubulars (sew-ups to most of the audience here) until the day I sold it - even when I brazed canti-bosses onto it and had used it for Cyclo-Cross.
In case you're wondering I still used Barum 'tubs' for 'Cross - but knobblies.
In those days one the few Barum stockists in the UK was Ken Ryall Cycles in West London - where I was regular customer - and I was a great fan of Barums which were an excellent compromise of quality and economy...
Ken Ryall will be remembered of course as the team Mechanic on the UK TdF team in 1967 when poor old Tommy Simpson bought the farm on Mount Ventoux...
Ian (bloody hell it's cold tonight in Luton) Luton - UK.