So if I understand correctly - you had these 6/7 speed Superbe Pro shift levers working correctly with a SunTour Sprint RD while running Dura Ace 7speed UniGlide on your previous bike?

And now you are attempting to do a similar setup on the new bike but this time with the older style Superbe RD?

I’m confused if the auto shifting is occurring in both friction and index mode?

If it is auto-shifting into smaller cogs on its own when climbing hills, this suggests that the D-ring is not tight enough. If you have tightened it up as tight as you feel comfortable with then you might need to run a corresponding tap into the shift lever braze on to see if there is some crud on the threads or if can be tapped a bit deeper…

BTW: those 6/7 speed Superbe Pro are some of the prettiest down tube levers ever produced. When run in index mode with a 7 speed SunTour “AP” freewheel or cassette, it should index great.

If no one mentioned it yet, SunTour AP freewheel and cassette spacing is not equal between all the cogs. The smaller cogs (bigger gears) have spacers that are less wide than the rest of them (I think I’ve got that right).