I'm surprised nobody mentioned the following little tip. When you break a bolt while torquing it, you're pulling the threads 'toward' you. When you do that, the upper threads on the bolt 'fuse' to the lower threads on the mount. Best way to get that out is to first tap it with a hammer to break that 'fuse' and then use vice grips to unscrew it. If you don't tap it first, you might drive yourself crazy by rounding off the bolt with the vice grips since those threads are under tension and virtually welded together. After tapping it, you'll be amazed at how easy it comes out.
One other thing - when putting bolts into an aluminum block, it's always a good practice to put a little bit of anti-seize on them. You'll get better torque consistency, and if you break something, it's pretty easy to get out.
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