I'm getting new alloy wheels

Can I use the old wheel nuts from the steel wheels?

Or are there special alloy ones I need to get?

The original nuts will only fit if the bottom of the nut is the same shape as the lip of the 'holes'. (ie they sit flush)

Aftermarket rims may also require a wider or thinner nut. I'd guess 'falcon specific' rims would be more likely to fit than those 'multi-purpose' jobbies.