Easy way to prevent metal shaving's from getting in the engine block (and I should have mentioned it previously) is to either magnatize your drill bit or apply grease to it so the metal shaving's stick to it. Even if you do get any in the block they are very easily removed with a magnet. Remember, your only drilling through a very thin piece of metal, not the block itself so your not making alot of shaving's.
Another thing to consider is that if you ever have to replace one, do yourself a HUGE favor and replace the old steel ones with new brass ones. The brass ones will not rust out like the old steel ones will and do not cost that much more. Most good auto parts stores cary both steel and brass freeeze plugs.