I have a DS Arms STG 58 with this same info stamped on the receiver. After seeing your post, I called DSA and asked these same questions about my rifle. I provided DSA with the serial number stamped on my receiver and they researched their records. DSA could confirm the date shipped,that it was a complete rifle ( rather than a receiver only sale ) and that it was an STG 58. They couldn't tell me how many LE/Gov't receivers were made. I have another DSA FAL ( a carbine ) which does not have the LE/Gov't markings; and, I can't see any difference between the receivers. IMO,there isn't anything special about the LE marked receiver. While DSA couldn't say how many LE/Gov't receivers were produced,I wouldn't think that such rifles would command a premium upon sale. However,if you're in law enforcement or a member of the armed forces then the "restricted" receiver might tickle your fancy.
I found the Customer Service reps at DSA ( Michael and Taylor ) to be helpful and courteous. Their turnaround time in responding to my request for info was very fast. Call them at 847-277-7258 with any questions. Thanks.