There are several outlets for bulbs that fit under your grille, that will take an HID bulb. I personally would stick with the 4-bulb setup and use a light housing from LMC or DDM Tuning. I would seriously consider purchasing the DDM Tuning HIDs for your light bulbs.
http://www.ddmtuning.com/Products/4656-Halogen-Lamp
http://www.lmctruck.com/icatalog/cc/full.aspx?Page=71