I am usually completely against re-stamping of any numbers on anything.
But what I see here:
You own the bike, its not stolen.
You are not trying to make a RGS out of something else.
Your not trying to cheat anyone.
This was something that should have been done to the frame 50 years ago, and was neglected to be done by no fault of your own. If the same numbers we are talking about now would have been stamped 50 years ago, we would not be having this conversation.
By going the "bureaucrat" route, and contacting this agency, and that agency, and hoping things will work out in your favor is a fools errand. If thats what you plan to do, STOP sticking money into this project right now and save your money, because it may not work out the way you want.
Or get some 1/4 inch stamps, drink a few beers and swing the hammer. Hit the restamped numbers with a sander to smooth and age them, and paint the whole works. Be done with this.
Lee