This will work..... as he has said, you can use a torch as steel does have a lower melting temp as cast iron does. You do need to keep the torch turned down on the temperature
so as to keep most of the heat on the exhaust stud. As it melts down, take a regular screwdriver, or pick and work the loose stuff out. I have never checked to see how
deep the stud hole is, just make sure you don't go to far.
I have also used my mig welder, and used a 3/8" fender washer, just be sure to
grind the inside of the washer hole, then place the washer flat to the head, and
turn your heat setting up to high, then go into the hole with the mig wire, and
fill the drilled out area of the stud, up with wire including the washer, then place
a larger nut to the washer, and fill with weld. This will put quite a bit of heat to
the stud, which should loosen up the rust, crud, etc, and you should be able
to remove it. Once it starts to turn....work it back and forth, and it should
come on out. If it breaks off, go back to the drawing board, and start over.
I have gotten everyone out, that the broken stud needed to be removed.