My Water Buffalo ('76 Suzuki GT750) had been fitted with an o-ring chain when I bought it. I probably would have done the same thing as an "upgrade." The increased chain width cut a groove into a plate that covers a counter-shaft bearing. It also temporarily affected the c/s sprocket's fit, causing a different problem. Fortunately, it was all easily corrected.
I suspect that many vintage bikes don't have enough clearance for o-ring chains.
That collection of wires under the counter-shaft is the switch for the digital gear position indicator. And it still works.
Bob