You may have to drill it and use an easy-out, but that's the path to hell because if the hole you drill is crooked or in the wrong place, you're f#c&ed. You break the extractor, you're f#c&ed. If the drill bit breaks, you're f#c&ed. Really any of these are still repairable but it's a matter of how much effort it is. At some point it becomes a better investment of time and money to source a replacement head.
Also, the original stud broke for a reason, probably the threads are siezed to the head due to galvanic corrosion (steel stud into aluminum head). Heat up the head with a propane torch and then hose the area down with penetrating oil. Repeat this a few times over the course of a day or two before you try to extract the stud.
There's also the possibility of welding a nut to the end of the stud and using that to turn it out, but if it's broken off flush with the head this trick becomes, well, tricky.
OTOH a decent machine shop should be able to get it out for you no problem. So if you have the $$ go this route.
mystic_1
