The other thing I noticed on this as well, and I initially wasn't going to post a pic of this because I wasn't sure if it was well known or not, but researching on google I found several mentions of it, including pics, so I guess it won't hurt anything to show it now. The top edges of the Magazine and front action screw box are filed down to allow the action to be more firmly pulled into stock. Even the spot of the bottom of the receiver is filed down as well.
Jack the Dog has a really good pic of his documented Marine sniper in this auction, and his trigger housing is filed down the exact same way. It also looks like it has the punch mark on the receiver rail that was polished over. But his is more towards the front of the receiver.
Here is a link to Jack the Dog's documented Sniper with pics to compare.
http://www.gunauction.com/buy/12918480