They are neutered AK's, which is to say for the most part they operate just like an AK but will not have muzzle attachment threads (which were turned down so that even if you did thread them, the diameter would be too small to use normal AK brakes) nor a bayonet lug. The rear of the receiver may, or may not, be able to take standard AK stocks. If it is slant cut, it was intended to mount a folding stock. As a result, you'd have to get a specially-made stock. Ironwood sells (or sold) them. They work fine but look a bit odd at the attachment point. If it is not slant-cut, you can take any stock designed for its specific type of receiver (stocks cut for milled receiver vs stocks cut for stamped receiver).
On the positives, the stamped receivers are thicker steel than European stamped receivers and so tend to be more rigid. Milled are, well, milled. The machining isn't stellar in the aesthetics department, but they are solid. I have owned milled Mak 90's and they were fine shooters.
