[Superman]

Make a jig, or get a jig (they're out there...at least one Pelicanhead has made them) to hold the drill bit in place. Without the jig, it will be very difficult to keep the bit from slipping sideways and scratching your head/exhaust mating surface. You'll need a right angle drill or attachment. I would suggest getting one or more reverse drill bits (these work in reverse....counterclockwise). Sometimes studs come out just from the drilling....they back out. But only if you are using a reverse drill bit, of course. I like the Snap-On screw extractors. A kit of ten extractors is actually pretty cheap.

Take your time. Relax and do not hurry, do not get angry.