How do I shave the cowl without screwing it up?

Edited: 4/26/2005 3:15:28 PM by MadMatt

I know the cowl is gonna warp bad if I weld it. How do other people do it? I've already shaved the doors, 3rd brake light, rockgaurds, mirrors, antenna, and gas door. I want to shave the cowl vents and maybe the hood squirters before I start putting my truck back together.