Randolph,

I don't want to throw a wet blanket on your party, but personally I haven't had much luck when it comes to drilling out broken exhaust manifold studs. Alignment is critical as you indicated. The hardened stud in a soft aluminum head adds to the difficulty (my opinion). A machine shop deals with these problems everyday and are actually pretty good at it. They are not always able to deal with them however if a lot of molestation (for lack of a better word) has occured prior to their attempt.

You would have to remove the head to take it to a machine shop. That isn't all bad. While the head is off they can go through it and check for plane, worn guides, replace the seals on the intakes and lap or grind the valves ("valve job"). You would basically have a rebuilt head when finished.

Either way take your time and enjoy the learning experience. If you are successful in removing the broken studs by drilling be sure to share your tips with everyone here as it is a common occurance.

Randy