I've had good luck removing finish from checkering with brushes. You might need to go over it more than once, or use stiffer parts cleaning type of brushes.
Tape a brush to a reciprocating saw blade to make life easier, or get a spiral brush and use a drill.
Your a hard man on checkering using the above methods, if your serious you may be related to the fella that Bubba'd the gun in the first place.
The checkering is machine cut not pressed, which is completely doable to recut by hand. If it was lazer cut as many of the new Winchesters for example are, now you have a problem trying to recut that crap by hand.
To the OP, removing the graffiti from the wood is doable by stripping the whole stock. Sanding out the engraving on the butt stock and recutting all the checkering panels with single line cutters to make all the panels look the same in colour and depth when done, as suggested where the engraving is you will cut a wee bit deeper. Sand the whole stock fill the pores, apply a finish of choice and it will look as good as new and better. The metal will be a more difficult issue in my opinion, I have no suggestions there as I am not a metal person. As for the scope that's perhaps the easiest part. Scrap the scope and those see through mounts, and replace with something more desirable and sensible.