OP: no way to tell what unit the rifle was issued to, unless u find a unit marking on it, from what i could see there weren't any, you should remove the top two hand guards and see what kind of marking/stamps you have on the barrel.
The matching serial numbers you have on the magazine and fore stock were added by a local unit's amourer, Long branch itself didn't stamp magazines or fore-stocks with the rifle's serial number; the local unit amourer's at the time did when the worked on the rifles to insure the magazines and wood went back on the same rifle.
that being said, if you need help identifying some of the markings, shoot me a pm with photos of them and ill be glad to help you out.
nonetheless, you've got yourself a nice looking LB there, one that is in excellent shape and should fetch a pretty penny being all original!
