I have nothing to add not being a cyclist at the time. I do have some info somewhat kind of related to the thread. I did not know where to list it. So, I put will put it here and it will get to the right place somehow.

I am putting new headset bearings in/on Campy Gran Sport/84 Lotus Legend Compe frame. 56cm frame so Columbus SL tubing. Here is the info. The fork has Columbus stickers but is stamped:
TANGE
MADE IN JAPAN 4B

That is it. It might be old news to some but news to others. Back to the content of the thread.