Driftwood,
Good decision. Take it from a Retired Gunplumber, you wanted nothing to do with that Navy Arms rifle. Unless you really wanted an expensive 3 dimensional wall decoration.
What you have heard in the woodwork is correct. The dimensions of the moving parts and the Geometry of the rifle is enough different,
nothing from today's guns fits. If something breaks, the only thing you can do, is find a "Happy Trails" that isn't retired to make you new parts from scratch. That can be a real expensive proposition.
You should however, avail yourself of a new manufacture "Brass" rifle to go with your "Iron" rifle. There is a rather nice example of a
Transitional available on the SASS Classifieds.
Coffinmaker
(Who still wants an "Iron" Henry)