Tom,
Cost to make this gun a good shooter (after you have it checked out) is $0. Just elbow grease and a mild cleaning. Sleeving is out as no one I know has 16 ga tubes. You can get a good idea of what gunsmithing prices generally are by going to Briley's website
www.briley.com. Forget the 2-3/4" shells as they are generally 1290 fps 1oz snot-kickers. Either reload or buy RST's short 16 ga shells. They are easy on the gun and the shooter. If the stock is tight now (no wobbeling when you flex it) just leave it alone. You really can spend a bundle on fixing up this gun or just enjoy it for what it is. If you want a really nice looking gun, hide in the bushes and learn as much as you can, get some expert opinions on every one you are considering, and get one that is right for the right money.
You just missed the Southern SxS with hundreds of Parkers for sale. That is a good place to look and get advice from the pros. for what to look for.
All the above just my $.02.
Carl.