Here's the general rundown of .223 mag compatability:
Bulgarian- They fit Bulgarian guns. I know they can be easily midified to fit Norincos, as I've used them personally out of my Mak-90 and seen the same mags used out of other Noricos. I've heard of them being modified and used in Saigas, but haven't seen it (though don't see why it wouldn't work).
Chinese- Polytechs fit Polytechs and pretty much nothing else (they're bakelite/plastic). They fit the Poly .223.
Chinese- Norincos fit Norincos (they're steel). They fit the MAK-90, 84s, and BWK-92.
As for Chinese mags in Galil/Valmet, I've heard both of them being used after mods, and everytime I hear about it, it's fifth-hand info from rumors. I'm sure it's been done with one or the other, or both, but I'd love to hear from someone that actually has done it.
East German- These were made for an EG produced .223 that was being considered for adoption by India. The Indias bought their own design (also an AK based rifle) and the mags for the guns have been sold off mostly here in the USA. They fit the Romainian SAR-3 like it wa made for it. Sometimes you hear about minor fitting required with one in 50 or so, but these have become the defacto SAR-3 mag. They are steel.
Russian- The Bakelite 5.45 AK-74 mag has been used with various mods in various guns. Reliability is questionable in the mods. It all depends on who did it, how they did it, and what gun they are running in. They're the orange AK-74 mags. They're dirt cheap, and easy to work with, but you will probably get better results using Bulgy mags for mods. Also once you take all the time and money for parts, etc to mod one to work, it's just about as cheap to but a mag that was made for the gun.
USA- M16 mags can be used in some guns equipped with an adaptor. The Galil is the first one that comes to mind. I've seen a Norinco that was modified for an adaptor for M16 mags. It worked great, and still worked fine with the original Norinco mags. The Hesse M47 shipped with an M16 adaptor. The big plus is that M16 mags are everywhere. The big minus is that M16 mags aren't exactly the strongest mag ever made. It's recognized as one of the weak spots in the M16 design, so why use a weak mag in a gun who's trademark is reliablity. Well, cost and not having to buy different mags does make some sense. I wouldn't have an AK that only took M16 mags (as some conversions I've heard about result in an M16 mag only AK), but being able to switch back and forth like the Galil, or the Norinco I saw, is a bonus.
That's pretty much the lowdown on .223 mags.
There are many more stories, etc of what will work in what, but these I have personal experience with.
If you bought steel Chinese mags, they are the right ones for your 84s. If you bought Polytech mags, you made a killing, because they are going for BIG bucks, and you could sell them and buy three or four Norinco mags for the price of one Poly. You did good no matter how you look at it.
The best mag for the Norinco is the Norinco mag. It's a no BS steel AK mag designed for the gun, work 100%, and you can still find deals on them like the one you found. Sure, they cost more than a 7.62x39 mag, but they are the best buy IMHO. The Bulgy mags are in there as well, but have been harder to get lately and take an actual mod to work.
Ross