90% of shifting quality is in the chain, the adjustment/setup quality, and the freewheel. IMO going to a 'modern' derailleur would be a 10% improvement. The old Campy NR shift well if properly set up. You are barking up the wrong tree.
Start by replacing the chain, lubing the cables, checking the derailleur ear alignment, and the adjustment. That should yield a large improvement. At that point if you want more improvement you could put on a modern twist tooth freewheel, which will shift better under load.
If you do, keep in mind that the bike probably has Italian thread hubs now. (can't remember for this model) You can cram on BSC threaded freewheels, but be sure to use plenty of grease/anti seize, and you won't be able to go back to italian.
Nuovo Record and Super Record derailleurs are exactly the same BTW. The only difference is the titanium bolts which save a few grams, and then anodizing on Super record.