I have a Remmy 870 20 ga. I am thinking about put a FF lll on. My question is should I have the standard drill and tap done and then buy the mount or should I have it drilled and tapped specifically for the FF lll? I have never had a gun drilled and tapped. I also have a Win. 1300 that came drilled and tapped and was wondering what kind of mount I would need for the FF lll. Thanks in advance for any help.