I've not seen it mentioned but FYI when I removed the brass plug from my 2008 S-40 the plug was somewhere between 2 and 3 mm thick or about 1/8" thick. Mine had a small dimple dead center on it which made it really easy to start the bit. I drilled with a small bit until the tip of the bit just started to break through. I used a 6-32 plug tap (For those who don't know, there are 2 types of taps, the plug tap is used for tapping holes that have bottoms and doesn't taper much at the end). A couple of threads was all that was needed. There is precious little space between the plug and the needle valve head.

Yes, that's correct. If you look closely in the pic above from my '06, you can see that there is a pinhole in the center before drilling.

Clearance to the idle mix screw is about 1/4" so it's important to tape off the drill bit to limit the depth.