Sounds like you want one for shooting long rifles only, and the current barrels are made for mags, and that's where you get the larger bore size. Sending it back to Ruger wouldn't work as they'd put on the same dimension barrel and you'd be in the same boat. If I were you, I'd buy one of the early non convertible single sixes, which would have the right barrel, and sell the newer one to help pay for it. Then, if you wanted the 4 5/8's barrel, have it shortened, which wouldn't be too expensive, especially compared to cutting down a 10-22 barrel like you're proposing. Just a thought.
HH