Mor-Kik,
I have one Armi Sport copy of a Spencer Carbine.
Never had a reason to pull the barrel, so I can't offer you much help where the threads are concerned.
But I have an original Burnside M-1865 barrel that is dismounted from the receiver that I can measure for you if you want.
Aside from that, I have found very few Armi Sport parts that will interchange with any original firearms they are meant to copy. I have also found that Armi Sport parts will often not interchange within themselves for the same Model arm.
Hope this helps?
My best,
Blair