You learned the hard way about hardened steel, huh? All guide plates are high-strength hardened units, and you will need either a quality cobalt drill bit or a carbide burr to enlarge the holes. Don't think that even a TiN (titanium nitride) bit will work. It might, but chances are you will burn it up too.
My personal preference is to chuck a carbide burr into a drill press and then slowly cut the holes up to the size needed. You could use a hand-held die grinder, but I like the control and slower cutting speed (LOTS less heat) of the drill press. Hand-held units also don't usually give you the most accurate results when lining up the bolts and slots when finished.
If you take them to a machine shop, most likely they would use a carbide bit of similar shape to a common burr and cut the holes with a vertical mill instead of the drill press. Only a different machine using a similar approach.
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David
