You asked about a "blow torch thing". I use my cutting torch to heat the bolts up red hot. Then let them cool a bit. Smack the head of the bolt with a hammer, or hammer and punch. They usually come loose. I turn them out a bit, then turn them in, then out, then in, etc. until it comes out. I will use some sort of penetrant to help. That will help break it loose to. If you just put a impact on it and try to back it out without working it back in, many times you will break the bolt off. Patience pays off when you get the bolt out without destroying the hole.
If the bolt extends through the hole and it can be reached from behind, sometimes I cut off the end of the bolt with a thin cutting wheel. That way the whole lenght of the bolt doesn't have be forced through the hole threads.
I have a couple of sets of screw extractors where you drill a hole first and then set the extractor in the hole and try to turn it out. Most of the time I have failures with them. Your just lucky when they work. The one that works the best is a set that comes with its own set of reverse bits. Sometimes a screw or bolt will come out while drilling the hole with the reverse bit.
