There is no one answer.

Paramounts were made for over 50 years.

There were a lot of subtle changes that add up. Different brake pull.

Side pull ==> center pull ==> side pull ==> dual pivot.

Recessed brake nuts.

I've been running an Ultegra RD on my old Colnago. I'm not sure the difference between NR 5s and NR 6s, but throwing to say 8s or 9s adds a fair amount of derailleur travel and relies on the spring to get I all the way back to very close to the mount. Repro long cages are available for NR RDs.

Anyway, lots of decisions on how to customize. All possible, but sometimes irreversible changes.