The stock just unfolds. It was, after all, designed to be used by illiterate peasants so you can be sure it's not all that complicated.
I think you are getting yourself confused over some simple terminology.
When Yugoslavia disintegrated after their communist leader Tito died, they broke apart into several different countries, one of which is called Serbia. Zastava was the state arms factory for Yugoslavia and is now located in Serbia.
In the past Century bought up a bunch of M70 kits and had DC Industries assemble them. Some of the receivers were made by NDS and others were made by DC industries. Both are considered to be decent receivers and the guns they built are well thought of in AK circles.
The gun in the picture on Atlantic's website is not a Century conversion as the receiver says "Zastava Yugoslavia". That means that the trunnion was made before the breakup of Yugoslavia and in fact it is dated 1985. It is clearly a kit build and it even says so in the description. I don't have any information on who built it or made the receiver.
Instead of asking a bunch of random people on the internet, why don't you call Atlantic and ask them who built that rifle? I seem to remember that Atlantic is having AK's built from kits on their own receivers and if they are, you can pretty much be sure that they are a quality rifle as they have a stellar reputation as a solid company with great customer service.
I have had one of the DC Industries built M70AB2t underfolders for many years now and it has had a buttload of rounds through it with zero issues. Even though I have several pre ban AK's and a few other newer ones also, I always seem to grab that M70 when I go shooting.