WCF,

You should consider drilling and tapping the rib for two 6x32 screws (or 8x32 if there's room), and put on a single Weaver base. Then mount a JPoint sight (http://www.jprifles.com/1.6.1.php). I've had very good results with this sight on a Freedom Arms M83 revolver chambered in 454 Casull, so I think it will withstand the recoil of the LC Smith also.

BTW, one of my favorite guns is the LC Smith my father left to me. Is is a 12 ga field grade gun much like the one you describe. Most of the color case hardening is intact, and there are no cracks in the wood. I'm planning to use it for ducks this year.