Per the previous question, it would help to know how the butt is finished now and how much extension you need. You can add up to 1-1/2" with a Silvers repro pad, and you can boost that a bit with black (or other) spacers between the pad and the butt. A good fitter can bend the spacers and the pad to fit the curvature of the existing butt, so there is no need to cut or square up the butt before fitting the pad. I have had this done on a couple of hammer guns and it works well for me. Keep the old butt plate and everything is reversible if you decide to restore the gun to original.
Another alternative is to have a wooden butt made up as a thick plate, rather than as a butt extension. I acquired an Elsie with this treatment a few years ago from one of the members here and its appearance is superior to that of an extension with a separate plate attached. This particular butt has a design carved into it and looks pretty good, but you could also just have it checkered.
