I'd suggest that you hook the top of bracket in place. Then use the bracket itself as the template. If the screws are sharp enough you probably don't need to drill any holes. If you can't make them penetrate the plastic bumper skin, drill small pilot holes. You don't want to drill anything too big.
I just got a slightly used 2008 with no front plate base, but the holes are there so the previous owner must've taken it with them. Given that the holes are already there, I'm assuming I'll probably need to tap in a couple of anchors to make sure the holes aren't too stripped? Also, it doesn't come with the screws, does anyone know if it mentions the size needed so I can swing by Home Despot?