Only way you would make this work economically nowadays would be if you had a decent barrel blank for cheap (unlikely) and do the work yourself, otherwise your better off buying a used single shot in 38-55. Youl be 500 bucks in the hole minimum otherwise on a snider, and it will be one heavy unwieldy club if the barrels contoured the same as the old one.......theres better guns to sink that money into.
You could possibly, make a liner out of an old military barrel. One poster here mentioned the brilliant idea of using swede 8mm rimmed barrels as a liner for 32-40, and you could possibly make an old 303 or 7.7 arisaka barrel work for 32-20.
Even then it would be a complete pain in the a$$ to load a shell in.
Turning it into a "Zulu" 20 gauge is just as good an idea as any.