[snapshot]

Those can be a nightmare.

But if you have access to a stick welder, you can take a short length of pipe the same diameter of the bolt head, hold it up against the bolt and then weld them together by putting the stick up inside the pipe. Once it's firmly attached, you can use vise-grips or a pipe-wrench to remove the bolt. The heat from the weld will help loosen the bolt as well.

Attaching the ground as close as possible to the stuck bolt is a good idea.

Good luck,

J~