The 07 MS tubes are used on the Sony 103x, 104x pjs, while the 12xx pjs are equipped with the 07MP(S) tubes, much bigger (sometime considered to be 8 inches, sometime no. mounted on the Barco 8xx series too).
The 07 MS tubes are the most widely used 7 inches tubes in the whole world. Sony, Barco (in the past, not in the Cine series, but in the 701, 708, 508, 600 and so on...), Electrohome (in the 31xx, 41xx, 35xx and 45xx), RCF (all the 7 inches pjs), SIM2(all the 7 inches pjs)... for example use that kind of tubes.
You cannot mount that kind of tubes on the NEC pjs. The NEC tubes are totally different. Taking apart that normally the NEC tubes are considered to be better (in image quality, specially in colors) then the Sony 07-MS, the major difficult would be:
1) the different size (the NEC tubes mounted on the 6/9PG series are much bigger, considered as 8 inches);
2) different shape and mechanical mounting;
3) different electrical parameters (like focus and G2 voltages, the anodic voltage is the same, 34 Kv...,AFAIK);
4) different color behaviour (you should change all the three tubes togheter, starting for the fact that you will need a lot of mods, on your pj...).
it's just a consideration/suggestion. Avoid to do that.
Romano