Might be "Rawbone", was that a typo or just illegible engraving?

Sometimes Wm Rawbone or W.G.Rawbone.

A restoration like this would normally include chasing or recutting the engraving, but probably not without some expense. Some of your countrymen may be able to recommend the best engravers for a job like that.

...and I too would recommend leaving the chambering as-is if the bore is shootable. Cases and projectiles are readily available, and Lee dies over-the-counter. Even a lightly-pitted or dark bore may shoot well with smokeless loads and jacketed bullets, and may actually improve over the first 100 shots or so.

With a single-shot you have the choice of the service load (heavy bullet at modest velocity) or the Express load (lighter bullet at higher velocity) or anything in between. The .450 calibre is great for hunting and fun at the range.