I own both the NP22 (10 years, ~20k rounds) and the Sig 226 Mk 25 (3 years, ~4k rounds). I own Norc, Mec-gar, and Sig mags.
Sig mags functional only in the Sig, they will not lock up on the mag catch in the Norc. Do not file these mags to fit, as they are expensive and will then be sloppy in the Sig as well.
Mec-gar and Norc mags function in both without issue, although you will likely be dissatisfied with how much play there is with the Norc Mags in a Sig. But they are less than half the price and do function perfectly.
I just spend the last 10 minutes mixing and matching the easy stuff.
Barrels, guide rods and recoil springs are fully interchangeable.
Sig slide complete will fit, function and fire with a norc lower.
Norc lower will not fit on the sig lower. Too tight.
I did not play with triggers. I can see some minor variations in tolerances on some of the trigger mech parts. Not sure if those are critical, and I had no interest in disassembling them.
Not sure what you are contemplating, but here is my take:
If you love the Sig, but can't afford one, buy a Norc. You can shoot it for years at about 1/4-1/3 the price of a Sig, and until you start competing seriously, you won't be able to blame your performance on the gun.
Your biggest disappointment with the Norc will be a rough trigger and underwhelming sights. To me these are instrumental to the learning process, but that is probably debateable.
If you are contemplating buying a Norc and upgrading the sights and trigger, then just buy a used Sig and be done with it.
Even though I have upgraded to a Sig, cause I can afford one now and really love them, I have no intentions of getting rid of the NP22 because its still a good enough gun.
Norcs are good enough guns, and at a great price. But it will never be a sig.
For the money you would spend trying to turn a Norc into a Sig, you would be better off just buying the gun you want, or buying two norcs, and having two.
The only thing you should be doing with a Norc is shooting it. I have put north of 20k rds through my NP22. I have beaten it up, and since buying my Sig the abuse has gotten worse. It still holds a tighter group in the vice than I can shoot on my best day with the Sig, and the only stoppages I have ever had have been user error.
Hope this helps offer some insight. If you have more specific questions, fire away.