If you can avoid drilling, do so, the magnet idea is good. Otherwise,
I've just used good, brand-name split-point bits with no problems. If
you get a chilled spot, you're going to have troubles and Asian
castings seem to have those. One hole will be like drilling pine, the
next will shuck the flutes off the drill. The only way to avoid
chilled spots to to anneal the casting and that's not going to be easy
to do without damage on a completed part. It should be done during
manufacture, but it costs money, so it's not one of those things that
gets done on import items that sell to a price.

Stan