Looks great John. Pretty close to the way I'd do it and replacing something so obviously missing is a worthy accomplishment for any vintage rifle.
I've got a fine 16 ga. sxs shotgun missing the monogram plate the entire 15-18 years I've owned it. Thanks for your offer but materials I do not lack...

Have you ever heard of shellac flakes? I've got some but have never used them. The notion is to make the plate removable with a little heat, but I don't know if heat would work with horn? or even how to use the flake shellac? Maybe why the Worthen plate fell out?
Perhaps a project for Dan one of these days?