Anxiety

I've some anxiety on exhaust header pipe replacement on VW 1302 Super Beetle, because some of bolts and nuts may stick dependent on thermal cycle on cylinder head for these 40 years.
Stud bolt defect may be very troublesome on earth in aluminum alloy cylinder material, how shall I remove the broken bolt from the head? Rusting and sticking are the main problem for the next task.
Replacement bolts and nuts are already prepared of course, but I don't know how to remove a broken inside bolt?
This barrier must be overcome at any rate no matter how I may refuse to do that. Immediately after running may be the better because of the differences of thermal expansion ratio.
Because of dusty powder and the anxiety above, I'm now in some hesitations.