A torch and some vise grips will fix the stud problem if there's enough left to get a grip on the broken off ones. Heat the ear of the manifold, not the stud, until it's red, and try to move the stud a little. It will probably move a fraction of a turn, and tighten up again. Keep up the heat/turn sequence until you can back the stud all the way out, then move on to the next one. Be patient! Once the studs are out, clean up the threads in the manifold with a tap, and install new studs from the FLAPS. They should be in the "help" section that most parts stores have. I'd reccomend changing all three studs, as the one remaining is probably pretty tired too.
If you can't get a grip on the broken-off stud, it's time to drill & tap. Just be sure to get the first hole (about 1/8" diameter) as close to center as possible, and work up carefully 1/16" at a time to 5/16". Then use a 3/8"X16 tap to clean out the remaining threads. Use LOTS of oil or tapping fluid, and work slowly, rocking the tap back and forth every half turn or so. An off-center hole will result in leaving a portion of the steel stud in the cast iron manifold, which is a sure way to break off the tap when you try to clean out the threads!
The above procedure works much better with the manifold off the engine, and clamped securely in a vise.
Jerry
