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!