@Grunk
The very bottom line of advice is generally any AK that is foreign built is going to be your best best. It will have the ComBloc barrel and should be GTG. The SN will be on the trunnion and NOT on the receiver. The receiver will have Made By, and the importers info.
If the receiver has the SN on it, it's a US made reciever. Doesn't mean it's bad...you'd have to ask specifically about which ever one concerns you.
This is a general blanket statement...there are some exceptions. But this should get you started...