Mark-

What exactly do you mean when you say that the bore is shot?
Do you know the minimum wall thickness of that barrel?
Do you know what the bore diameter is of that barrel?
What are the chamber specs?
What is the barrel outside diameter where your bore measurements are?
The reason I ask is that our friend Steve (bouldersmith here on the site) represents Teague - and can get you set up with a full-length sleeve/line job - and you could continue to use the gun as a shotgun OR a smooth-bore roundball rifle (if there's enough meat where it counts...)

Start there, then we can continue this counseling session!

Sweet gun by the way.
I'd definitely be proud to have it myself!
I can see why you would want to preserve the external contour and continuity of that damascus barrel.

Cheers
Tinker