Warn your powdercoater; these are fairly porous castings and outgassing can be a problem. If they bake them for a while, before powdercoating, it will minimize the chances of outgassing during the post-powdercoating bake.
As an alternative finish, try Cerakote. It does not need to be baked, so outgassing isn't an issue. I've used one called CERAKOTE GLACIER BLACK. It's a semi-gloss black and looks just like semi-gloss black powder coat. It's also rated to 1,800° Fahrenheit, so it's great for headers and brake calipers.
