I have a cosmopolitan motors catalogue from the early 80's and they (non leading axle) are shown there as dirt track forks. Pretty sure they were available earlier than that, at least 77 on but my gut feeling is they may not be types that were available pre 75. That red Marzocchi stuff is around late 70's from what ive seen You would just have to try an find some older catalogues or ask on euro forums or something.
