I did not read or catch that the frame derailleur hangar was checked for alignment with a tool such as to set up index shifting.
I would start there if applicable.
I am also assuming the wheel is the correct measure for the hub.
no excess slop in the mounting pivot.

these mechanisms are pretty stout, possible the parellogram is tweaked, not easy to do other than stuffing the cage into the spokes.


I was given a Nuovo Record mech 40 years ago, was performing poorly, had a twist, variable effect on performance, really depended on the cage orientation. had or made the tools, it was slightly twisted. risky to correct but what to lose? Time in the shop, a mill and a lathe, leverage.