What Pendergast runs is not a typical 4-3. It's an old school Buddy Ryan defense. The WLB is like a 3rd defensive end (i.e. someone who would typically fit as a 3-4 OLB). Unless he's the Mike, Vrabel would be that guy as of right now.
And I'm pretty sure the Chiefs are going to roll with Pendergast's system in 2009, but with the idea of converting to 3-4 in the next year or two. It's going to be like a stop-gap since a lot of the players that fit in Pendergast's system are also great fits for a 3-4.