Mark Sam:  The marks on your stock are an inspector's "cartouche" with the Inspector's initials and year of acceptance (probably J.S.A. = J.S. Adams).  The Circle stamp has a stylized 'P' in it for "passed".  Your stock is valuable because it is early and unaltered (ram rod groove not filled and 'flat butt plate').  The "pins or shim" are the remains of an early style magazine cut-off.  Don't mess with the finish of this Krag.  It is an early one and untrained efforts will destroy its value.  Get some Krag Books, at least Joe Poyer's, "The American Krag Rifle and Carbine".  You can get this for less than $20.  Early Krag Rifle Rear sight and Early style cut-off come up on eBay for not too much money.  Go slow!  You've had it for 40 years.  Don't ruin it now.