Go to Vortech supercharger's site and and download the instructions to install a Ysi on a 5th gen. In the instructions, you'll see how and where they have you drill the pan for an oil return.
In the parts list, you will also see the bit they send with the kit for the tapping of the pan.
Edit:
Here is the download link and you want to read Part 5 which starts on page 22.
From the parts list, you need a 9/16 Roto Broach and a 3/8 NPT tap (or whatever size tap you want to use that matches the fitting you want to screw in)