hmmm...
If you have access to a machine shop and the skills to do it, it might be cost-effective, though I'm not sure what the thickness of the barrel wall is if it's a cut-down barrel.
Do you still have the original 9"? That could tell you if there's enough metal for a choke. Do you have the choke tube(s) you'd want to use?
If you have to pay someone to do the machining, and you have to buy tubes, it might not be cost-effective, unfortunately, even if it's feasible.