With all the information that is given here, it would be foolish to alter it. The question now becomes what to do with it. Is it a collectors piece, is a just a barrel to be used and just what in eveyones opinion would the value of this be? Any ideas?
Several good questions, but not easy to answer. Value could be established by putting it up for auction.
I paid $150 for this barrel that I wanted for my collection and to use to illustrate how GRRW marked the barrels they sold individually. But there may be someone out there that is willing to pay twice that for yours. I've seen other vinatage barrels sell in the $300 range.
If one wants to build a rifle around it and still preserve the markings, I can think of a couple of options.
I believe it was Herb Troester that used a spacer, think of a thin washer, between the face of the breech plug and the internal shoulder of the threaded breech. This way he didn't have to file off the markings to get the breech plug fit and the timing on the flats he wanted. He adjusted the thickness of the spacer. Of course, if one uses a patent breech, it will cover the markings. If a flint plug and tang is used, some of the markings will possibly show.
Another option if the threaded section of the breech is deep enough, like 5/8", is to cut off slightly less than 1/8" of the end of the barrel with the markings and save it with the finished rifle. If the rifle is made with a patch or cap box, this piece could be inlet into the cavity of the box to document that it is a GRRW barrel.