Most of those rusty old guns should be hung on the wall and never fired again. They are potential IED/pipe bombs. Also, having any sort of work done on them can end up costing more than the gun is worth. I have said before and I stand by it; most Damascus guns should no longer be in use. No gunsmiths I've ever met will certify them as safe any longer.
As Rich said above, relining to a smaller bore size will make the barrel heavier and thus the gun will not handle as well as it once did. Then again, I've hunted with several inexpensive shotguns that handled like a bar of lead. The things I killed with it didn't seem to notice the difference between my clunky old Savage 311 and a Purdy costing thousands of dollars. If the choice is between never firing it and getting it lined so you can fire it, albeit with less ease, maybe a clunkier barrel is a viable option.
That said, take it to a competent gunsmith and ask him what he thinks. Listen to what he says and follow his advice. Unlike us here on a forum, he IS potentially on the hook for damages if he certifies the gun as safe and it blows up in your face.... which is one reason why most gunsmiths will not certify marginal old guns any longer.
