The Ruger MKIII comes drilled for the supplied mount. It's a nice setup but with the Red Dot or scope installed the iron sights can't be used.
Another useful setup for the Ruger with a bull barrel is installing a rail under the barrel for a light or laser/light.
I installed this rail a couple years ago for inexpensive laser/light practice and it's become one of my most useful guns. Not only is it great for day and night practice but it's handy for walking around the place at night.