Heres a shot of the Unity 6" spot installed on a 51 1 ton.
Tried a 5" but it looked kinda wimpy on tis big truck.
Didn't encounter any wires when drilling the post,but the dome light wire might be there,so proceed with caution!
http://thumb15.webshots.net/t/52/552/4/69/84/2212469840103393295UNpAxq_th.jpg