I am trying to trace the history of the low number SA 1903 I have that has been through several rebuilds. I believe it is a USMC receiver as it has a hatcher hole and marks on the barrel and receiver that look like they came from plumbing tools. Can anyone point out reference materials that might help me. I did find a web page with serial numbers for USMC rifles and mine falls withing a range listed but is not specifically listed. TIA.