Leave it alone and shoot it. Please.
JR
Bad plan. Period.
The gun is 100 plus years old, and, Im guessing has NEVER been apart for a strip and clean, or, had fresh lubrication, in the correct amount, applied to the internals. Looking at the head of the stock, from an internet picture, for chrissakes, it appears dark, and in need of some oil removal.
Dell Whitman. Paul Hodges. Kirk Merrington. James Flynn. Get the gun in for its 100 year service. Any one of these guys could work on the buttplate, or, might have a nearly identical one, in far better shape, removed from a gun that got a pad, or, they likely know where to get one. A better horn buttplate doesnt have to mean new. Even the rusty looking spots will look better with a strip and clean.
That is a good gun, far above the grade and value of amature gunsmithing, and worth the investment of a craftsman doing some maintenance. I doubt these guys would attempt to drive a 100 year old car without looking, hard, to see if it was in need of some upkeep, but, they are telling you to do the same with a very valuable gun.
Good luck.
Best,
Ted