Burris FF lll Mounting Suggestions

[Punisher]

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.