The original Mosin Nagant PU scopes did not have an adjustable field of view so sighting it in had to be done by grinding the mount (or alternately shimming) repeatedly until zero was acheived.
There are now good three post PU repRo scopes that have an adjustable FOV so in my opinion, this type of setup has become much more home-doable.
I have broken off a tap in the hole and although it took me hours to grind it into pieces without damaging the threads, I was successful in restoring an ex-sniper.
Keep in mind Ex-Snipers are HARDER to restore because the old holes are welded shut and welds cannot be re-drilled, only ground away. You are better off, if you aren't trying to put an authentic one together, to buy a non-ex-sniper to make your repro.