finding a barrel will be an issue only option is to get one from alliance (bit dear imo)or get one from gmac in 24" and either have them do the machining or find someone else to do it
getting the original barrel out will be fun and will either involve heat and collets or easier to just cut it off and have the remainder machined out
I have a drawing for the spec on the leade into the barrel
far easier to get a new style steel breech then all you nee to do is get the 24" barrel from gmac cut to 14 and recrowned