The first step is to have the life of those barrels determined by a gunsmith with a bore scope; why were those barrels swapped out by their former owner(s)? If you have concerns about their bore life, it doesn't seem reasonable to waste money on barrels that might not be as good as the one you already have. Each barrel would have to be installed on your receiver, and adjusted for headspace by a gunsmith, which accounts for perhaps 30% of the price of a new barrel, but you'd have to pay for it twice if there isn't much life left in those barrels. IMHO, a better bet is to get a custom barrel from one of the good Canadian makers, Ted Gaillard, Ron Smith, or Bob Jury, order it with a slightly heavier contour so its not as whippy as the factory barrel, and you'd come out ahead in terms of cost and quality.