As Feets said, you can get the extractor out with a punch and hammer. Once you get it out, if the hole you drilled is on center I'd keep drilling until there is nothing left of the bolt other than the threads. Get them out with a pick. If the hole is off center, use a Dremel to grind it back on center and then drill. If all else fails HeliCoil it. But again as Feets cautioned, don't go into the water jacket.

I've done what I'm recommending a number of times so it does work.