I doubt that the thread on the barrel is a standard one, so check this carefully. If you are going to use a die to cut the threads, as opposed to cutting them on the lathe, you will probably have to use a tap on the frame as well as a die on the barrel. If so, be careful to not to not remove too much metal.
Usually in a case like this you only have to remove about 1/8" to 1/4" of the barrel at the back. If you are looking at something like 1/2" I would buy the new barrel, and then "age" the finish so that it would match the gun. Cap & ball black powder shooters do this to their revolvers all the time to make them look more "Western."