Couple things if I may .
I would start looking at period muzzle loading SXS. Pay particular attention to the transitions from Lock mortises , both as the come off the wrist and climb to the tang .
Add on to that the diameter of the wrists . Lines of the comb and flow of the forearm
In doing so , your going to see that you can remove a lot of wood from your CVA stock . The reason I mention this is once you file the lock plates and tang down they will most likely set to low in the wood . Unless of course the cast engraving is very shallow , like the others have mentioned .
For the most part the lock plates and tang will be soft enough to file . In fact most times they are so soft that the plates can easily be warped by simply over tightening the screws . IMO about like mild steel .
Myself I would simply file off the cast engraving and then stone the plates so you can engrave .
Now there are acceptations. On some pieces ,the cast engraving is very deep . Very near that seen on some TC’s . if that’s the case then keep in mind thinning the lock plate to the point the castings are removed , will make the plate weaker then it already is .
So you some judgment there .
Now I know you didn’t mention the barrels . But you may be thinking about doing some engraving on them as well .
So ill mention this as well .
For the most part most folks hold the opinion that the barrels will be rather soft . don’t bet you pay check on that . While I have worked on some that the barrels did feel soft while engraving , thus cut like butter . I also have worked on some that were un believably hard . So hard in fact that even my cobalt gravers struggled .
Anyway , back to your question .
Another thing to keep in mind is that when working on CVA’s you never know what your going to have to consider .
CVA made 2 types of SXS . A field grade and a so called presentation grade . The only real difference I have been able to see is in the amount of engraving on the locks and tang .
Field grade has very little while the presentation grade has a hunting depiction with more relief
Another thing would be concerning the tang itself . Most times the edges of the tang are strait down . There will be no under bevel .
However other times the tang will have a bevel . But in both cases the inletting is machine done . As such the inlet walls are strait down and do not match the under bevel of the tang .
So look closely because if your inlet is tight now and your tang has that under bevel .
Filing the engraving off of the tang can open up the inlet.
so look closly at what you have and then go from there .