Lots of heat and use tool steel drill bits or cobalt, the danger is slipping off the harder steel but so long as it has a decent pilot hole and you go slow will be no problem, had to do this on cozmeisters head bolt as someone had chewed the bolt head up, went up 0.5mm at a time took about 45 mins but did the trick.
A pillar drill really helps a lot if you have one.
You will always get corrosion between steel and alloy, this is called differential metal corrosion, quite normal just soak in grease coppaslip or similar, try to exclude all the air being able to get to the bolt threads etc to stop in future.
tabetha