There's guy named "Different" - (Lee Emmerson). Writes books on the M14 and he has a magazine guide. Things like number of spotwelds along the front, markings, (even faint) on the lower rear edge of the magazine. All tells whether or not it's USGI. He posts a lot on m-14forum.com and can point you in the direction of finding out exactly where it's from....Neat find.