If I remember correctly, a 1/16" punch, I've changed out probably 30 or more CZ front sights. You don't drill the new site base, you grind it. I use a dremel cut-off wheel, but you could use a triangular file.
Install the new uncut sight and use a 1/16" drill bit twisted by hand, or in a hand held drill bit holder to scribe where the new groove is to be cut; be sure and mark both sides. Or use the same punch used to remove the roll pin to mark or index where you need to grind the bottom groove on the new front sight.