Well I've laid out the pads for the pins. I didn't need to change the spacing between them, just how far apart the two sides were. I then added the heat sink pad in the middle. Took forever to get everything centered and positioned properly. I rounded a few of those measurements that were between two values to the closest whole milimeter. So I made the package body 11mm long and 6mm wide.
But the heat sink pad, while not wide enough to touch any pin pads, seems awfully long. It touches both ends of the IC. None of the pics in the datasheets show a heat sink that large. he just have a small area in the middle of the chip. What's up with that?