Propane is usually not enough. I use a MAPP gas torch with good results. Get the stud HOT with the torch, then put a pair of vice-grips on the stud. This will act as a heat sink and shrink the stud quickly, often breaking the grip of the stud to block. Your favorite penetrating oil can't hurt.
Oxy-Acetylene is best, but not all of us have that luxury. As for the flush one, center punch and drill it out. Start small and work out with bigger bits until close to the threads, then work it out with an awl or pointed screw driver.
Stay away from the exhaust cover screws if you can help it. Those break easier than the head bolts.
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