I just got done repairing that area on mine a few months ago. First off, like they said above, its upside down in the picture. If you look closely, you'll see that the contour of the top matches the door pillar. Kind of. The rocker fits over the bottom of it, so you won't see most of it when its all in place. The flange with the holes is for the bracket thing the front fender bolts to, the back hole is one of the cab floor brace holes.
That said, I don't have any good pictures for you because my pillar was so far gone and the part was so poorly made that I fabricated the bottom half of the pillar from scratch and cut up the door pillar repair piece to get some of the more complex curves. It just didn't fit with the rocker at all. I wound up welding the rocker to the bottom of the pillar.
Heres the pictures of my cab repair so far, maybe they will help a little.
http://s140.photobucket.com/albums/r28/meld1234/Davids%20Truck/
