I have no input on collectors value, but what exactly is counterboring as applied to a Krag?
I have seen a report of a test on crown angles and changing to all the trick angles made no difference in accuracy on a rail gun. So doing a large counterbore like .375 diameter and .375 deep to make an 11 degree crown inside the 3/8 hole would be a waste of time and really show something had been altered.
Seems like one could bore or ream the last 1/4 inch to plus .002 over the .308 bore taking out all of what is left of the rifling and leave the existing crown. Looks would not hardly be changed except the last bit of the bore would be shiny with no rifling. Maybe the pits are deeper than that?