Yeah, I will polish it up and cold blue it, probably many applications, to try to match the barrel color.  I have a product that produces a finish that's almost black:  "Blue Wonder Gun Black".  I've gotten good results with it before.

Thinking again about how to attach the sight base, maybe I could just use solder like on the front sight bases of many Mausers.  The fit is close enough I should get a good bond.  In that case, of course, I won't even try to fill in the dovetail.