I put a 2 1/2 X pistol scope on a .30-06 NEF Handirifle a number of years ago and it worked well. For some ridiculous reason I sold it, silly me! The pistol scopes are designed to accept the recoil of handguns, a muzzle loader rifle would kick w-a-y less than that.
I would suggest using duct tape or similar to position the scope on the barrel so you can practice mounting/dismounting the rifle to make sure you have it within the eye relief distance. Otherwise you will moving your head back or foreward on the stock to get the optimum view through the scope. With the tape you can reposition the scope until you have everything in the best position when you take a shot. Then make sure the gunsmith maintains that position when he drills & taps the barrel for the scope mounts.
-WH-