Indexing aside (as noted above, it won't), the issues will be that the spring in the RD will only push the RD a certain distance to the right (high gear end) ... how far it will push the RD will vary with the thickness of the gear hanger. Typical rear hangers in the 70s were about 5 or 6 mm thick - typical hanger now might be 10 to 12cmm thick. Conversely, the top sprocket will in many cases be closer to the right hand drop out now than it was in days of yore.
The spring in the Nuovo Record RDs works against the middle of the plate on the back of the derailleur parallelogram and in many of these older Nuovo Record RDs, that plate ends up slightly bowed out.
The nett effect of all of that is often that the RD doesn't have enough travel to the "outside" to get you into top gear, especially on the road (it might "just about" work in the stand.
Going the other way, you need a lever that wraps enough cable around the heel of the lever to draw the derailleur across it's full range of movement to the left - with 7s on the original Campag lever, using an" Ultra 7" freewheel, to go from top gear to bottom meant moving the lever through about 120 degrees and a U7 freewheel was / is just about the same width as 7/9 of the 9 speed sprockets.
Simplex Retrofriction had a bigger diameter heel than the original Campag levers, and IIRC, Campag Retro 2 were bigger again, so would probably best suit a 9s cassette ....
Now, you might find that the full range of lateral movement of the RD is not enough to get bottom gear, especially if it's a modern frame with a thicker dropout / hanger as the gear will start further out to the right than it was originally designed for ... if it's an older frame, you'll run out of movemnt when further left than you will with a newer frame, so you may and may not be able to get to bottom gear for that reason - the limit screw may be screwed all the way out but the limit surface (that the screw normally impacts to stop the movement) may be in contact with the part of the RD thhat the screw passes through, before you have acheived bottom gear.
In any case, as is noted above, depending on what rear hanger you have, you may and may not be able to work to a bottom gear bigger than 26 - Old Skool vertical dropouts from Suntour, fior instance used to allow a tooth bigger bottom sprocket than Campag road ends ...
HTH
Graeme