It will cost you more to ream the old barrel than it would to buy one new direct from Remington. I believe that's what others have already said, in different words.Fred Fuller - The serial number has the "M" you mentioned. I bought the barrel new in 1980, but I have no idea what the barrel contour would be. An opinion of a shotgun-smith would probably be a good idea.
oneounceload - I am going to price used barrels and see what I come up with. Just in case I feel that the prices are too high, can you recommend a reputable shotgun-smith that would give me an honest opinion of the chamber reaming in my barrel and a fair price for the conversion?