"Rifling and modern ammo" is absolutely not your problem.
Your barrel might be corroded or just plain dirty and your stock might not be well fitted, but a 10" twist barrel has been working fine for over a hundred years and nothing is going to change that. (But don't think you are automatically entitled to MOA accuracy just because of gunzine propaganda. 4" is pretty sloppy, but 2" is not bad in the real world.)
What is your sighting system?
Do you have pictures?
If a scope or commercial receiver sight has been installed, and if the metal has been reblued, a return to military configuration will be expensive. Even if it has the GI sights or some sort of no-gunsmithing scope mount and is still Parkerized, it is likely missing a lot of the military hardware.