FAC is selling AK receivers that aren't OOW...they say they're a little thicker which make me think they're Arsenal receivers? I know trunions need to be thinned slightly to fit inside it..

My question is this: Does anyone know where serial number/other information is placed on them? If they're in a sane place, I'll purchase two, and have one turned into a sidefolder. Otherwise, I've heard OOW recevers can be made up into sidefolders...any other receivers?