I am not knowledgable to comment on the proof marks but after reseaching it seems that a driving factor for the 8x60 seemed to be the option to rechamber rather than rebarrel. I suppose we may never know for sure on this rifle, but I have a box of 8x60 mms and hope to shoot this rifle soon.
It has two rear sight blades. Would this rifle be set up for 50 and 100 meters by chance? I guess I will know shortly.