If all else fails, heat it (if you can).
My flywheel bolts had been ground down 2 engines ago by a previous owner to clear the clutch. (I guess they were being ultra frugal and had the flywheel machined down to a (thousandth-inch
) of its life..
There wasn't enough hex head for a socket to grab. I used a body grinder to grind the heads off, thinking I'd just pull the flywheel off and then use visegrips on the shafts. In the act of grinding, I unintentionally heated them up enough that they started to spin out...
My dad made a career out of removing broken bolts and screws (rebuilt steel power plant pumps which were immersed in sea water). While he was a machinist, the first tool they all grabbed for whenever it was time to take anything apart was a torch.
good luck, and don't work on it while you are tired.. a goodnights sleep, and sometimes these things become child's play.
brian