[flatheadmurre]

The idee is to get enough heat into the part stuck in the block so it expands and then cooling down frees up from the block.
So which ever metod you use make sure you heat it hot and long enough for the heat to reach down into the entire bolt.
Then let it cool down so it frees up before trying to loosen it.
Its not only that you want something welded onto it for wrenching...you want the heat to break it loose for you to.