Those look very nice and you should be proud of your work. For a finish you should probably decide on the intended use of the pistol with them mounted. An Danish-oil finish can sometimes break-down under heat (like hands) but a polyurethane can seem "slickery". You might consider using some of the Birchwood-Casey rifle stock finishes; they are made for firearms use and their stains can be controlled easily. Good luck with your project!
"History teaches that war begins when nations believe that the price of aggression is cheap." - Ronald Reagan