Well, there were "Japanese standard" downtube bosses and "European standard" downtube bosses back then. Shimano offered shift levers in both standards if you knew who to ask. The "Japanese standard" is much less common since it only appeared on high-end Japanese frames of the '70's and '80's. Let's see you find Campy shift levers to fit those bosses.

I remember sorting out the packages of Dura-Ace DT shift levers into the two types back at Euro-Asia Imports. I bet there's still some of the M4.5 hardware kits sitting there.