Huvius:
The correct repair may be to install larger-diameter discs, but the position of the locking screws doesn't give you much room to move (if you want to retain them). This was probably not an uncommon repair IMHO, as I have seen several DRs over the years with overly-large striker-discs, including a .470.

As for the vertical mark, no idea. Would need to establish what it actually is before suggesting remedial action.