US Krags are not serialled anywhere but on the receiver. However, some of the mods noted are scary. What do you mean by "changed" to a buckhorn sight? (I know what it is, the question is has the barrel been dovetailed to receive same?).

A Boyd's stock will seriously downgrade the value of the rifle. Far more acceptable - and much cheaper - is the replacement of only the forend, concealing the joint under the band. While not as desirable as a proper military stock, it does preserve what is left, and changes the end result more towards a "repair" vs. a "fake".

Not sure of your ultimate goal, but - depending on what has been done to the barrel - you might want to look further. If I knew the price of what you are buying, I could make a better assessment. You're already looking at a few bucks in missing parts (sight, handguard, upper band assembly) too.