But whether they are reducible to mental event is the question. (And how are mental event in space, anyway?) Isn't physicalism a kind of materialism? Can physicalism be true, and materialism be false? And what makes you think that abstract objects are "in the mind"? If numbers are classes, which seems to be true, classes are not in the mind. So numbers are not in the mind.

Mental events are in space-time because the mind is the brain, and the brain is material, and the brain is in space-time. It's not that physicalism is a type of materialism, but materialism is a type of physicalism.