Yes they are suitable for alloy, in fact Porsche use them on every thread in there engines i believe.
As for clean and straight, make sure you get all of the snapped off/damaged bolt out first, use ezi-outs if necessary. if its in a tight spot in the engine bay then remove that part or pull the whole engine out so you can get a cleaner finish.
Just start off gentle, if your really worried then tape a small level to the drill to keep the angles right.
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