Charlie,
I can't remember the CCNL# but I think it was in the 330's that has the log of WRA stamped recievers. I'm not at home right now to get you the info, but if someone doesn't get it for you PM me and I'll find the article number. IIIRC it was about three weeks after the receiver was numbered that the carbine was assembled give or take depending on what was going on at the plant.