Francois:  Look for a "P" on the barrel below the wood.  Also, look for two small circle 'spots' on the top of the barrel (8 1/2mm and 14 1/2mm) in front of the action that show a faint difference in metal finish (holes filled with finished off screws).  If these features are absent, the barrel must be a non-Krag replacement.
     Any Lyman, Redfield, or Williams Sight Disc should fit your Lyman rear sight.  For Hunting, these were left off to improve field of vision.