Thanks. I got some help offline from another member and am just beginning to develop a grasp. Here's a couple of pics. Pictures are large, so they take awhile to load. In the second picture the safeties are grouped 1-2 (left to right, top row) and 3-4 (l-r, bottom row). #3 is much shinier than it looks in photo. #4 has slight linear marks and #1 has faint circular marks. Opinions and reasoning behind them are welcome. If any are USGI I'll be looking for opportunity to swap for other parts, but will give my offline advisor first crack. Thanks.

http://s4.postimage.org/e9uui-31a61763-resize.jpg

http://s3.postimage.org/KQivi-31a61763-resize.jpg