I also own an NP22 and had an NP29. The NP29 was modified to accept a GSG 22lr conversion unit. I had to file down the ejector a little so that the magazines could be completely inserted. I also had to polish the inside of the frame where the slide stop is to make it possible to install the slide and barrel assembly. I also needed to change the original mainspring (23 lbs) for a reduce one (19 lbs) or else I was getting FTF and FTE. As you can see it was not a drop fit but after 4 hours of work with a file and sand paper, it worked beautifully. My NP29 trigger was terrible when I got it so I had to polish the trigger bow, trigger channel, the disconnector face and the leaf spring as explained in the AGI videos. The extractor did not have the correct tension either and I was getting FTE once in a while. After filing and polishing the angles and bending it as explained again in the AGI videos, I never had any FTE. It was a good gun, but not out of the box, and if I had to pay a gunsmith for every modification I made, in all honesty it would not have been a good buy. But I really learned a lot with this gun. I recommend getting a copy of the 1911 shop manuals by JERRY KUHNHAUSEN to know how to fix these 1911 pistols.
My NP22 is a different story. This is the only Norinco I got that did not required any modification or tweak to function properly. (I own others Norinco, like an 1897 and two 1911 .45 acp, all of which required some care to function properly). Its only problem is a cosmetic one, where the relief in the slide for the barrel to cam into is crooked. It does not affect function nor accuracy, but it is not a SIG fit and finish. And I must agree with others about the grips, you have to change them. The conversion unit for the SIG P226 does not fit on the NP22 frame, and unless a competent gunsmith mill the slide, you probably can't make it fit yourself.
I find that Norincos are good guns for the money, but in my experience, if you are not prepared to tinker with them, you might be disappointed. Sure, I only got a limited sample (5 different units), but 4 of the 5 required not so simple tweaks to be reliable... My latest purchase was a used Remington R1 and there is a day and night difference with the nork. I always read good things about the SAM (Shooter Arms Manufacturing) vs the Nork, but I never saw nor handled one but may be of interest to you.