Lloyd, it would help if you could post the dimensions of your broken buttplate with max width, screw hole locations and spacings, etc. as SxS 40 requested. Even better would be a picture of it laid on 1/4" or 1/8" grid graph paper. I could then look though my box of vintage American double shotgun buttplates too.
I could glue that thing back together and you would never know it. Colors and textures wouldn't match? Besides who would care what that butt plate would look like anyway? It's already a little rough. I have put too many things back together with JB Weld. And you wouldn't have to paint it. All you have to do is glue the pieces back together and leave it the way it is. Have fun fishing Lloyd. And like you said, it won't be that hard to fix. I would keep it original unless you can find another original one. But good luck.
This sentiment is precisely why I spent time several years ago planing and gluing pieces of walnut together in order to find which adhesives would provide the most invisible repair joint.
Of course, I never even considered JB Weld or any other gray or white epoxy. I already knew how bad those repairs looked. It was because of seeing so many of those crude and ugly glue joints on guns that I wanted to know what would give me a repair that didn't look like it was done by a blind monkey. I have seen plenty of gray epoxy repairs on stocks, buttplates, or to fill the gap between the ribs of shortened barrels. Also used as stock bedding compound and even to attach sights. None of it looked good. Gun work like that doesn't even qualify as amateurish. And it wouldn't be suitable on anything except a cheap barn gun, or maybe a temporary repair until a suitable replacement part could be found.
JB Weld is one of the better general purpose epoxies out there. I find it useful for many things. But gun repair isn't one of them.
