Also drilled into the bolt and try to "grab" it with a bolt extractor, which broke inside the hole I drilled.
If necessary, pay someone to weld the nut on and hope there is enough of the bolt to weld to. Trying to MIG weld to a hardened extractor is a PITA.
Please don't take this personally. I'm saying this for the future benefit of everyone reading this thread. Do NOT ever use extractors, not ever. With very rare exception, it will break and make the problem worse. My personal opinion is the bloody things should be taken off the market.
Here's how to remove a broken bolt if you do not have anything sticking above the surface to weld a nut to.
Very, very carefully drill a small hole dead center through the broken bolt/stud being careful not to drill into the block/head.
Now pick a slightly larger drill bit and drill through the same hole.
Repeat the process with increasingly larger drill bits until you reach the point where you have removed the metal to the point where just the bolt/stud threads themselves are left.
Use an icepick to work the remaining bolt/stud threads loose from the threads in the block/head. Be patient. A small pointed punch can also be used. Once those threads are worked out, you can run a thread chaser in the hole to clean it up. Do NOT use a thread chaser for head retainer bolt holes in the block.
There is one other thing that can speed this process and that is reverse (left-handed) drill bits. Here's why, if the drill is running backwards there's a decent chance that at some point it may actually spin the remaining bolt/stud out of the hole.
Clear as mud? �

Larry