Thanks for all the suggestions. Fortunately the casting metal is quite solid and I see no signs of ZP infestation
I think I'll try a self tapping screw in one post first. One problem with tapping is that a bottoming tap is something I don't have, and I don't want to have to make a hole deep enough for a regular tap.
I have regular taps but need bottoming taps for 4-40 and 6-32. Anyone know where I can get just those two taps without having to spend $50 or more for a whole set.