I am in the process of doing this now on my 4x4 Burb. What a job. I took a bunch of measurements then cut everything out. I started with the foot well patch, then front and rear door pillar patches, then front and rear cab supports, then the floors pans out to the rocker. The prefab patches were mediocre at best and require some work. Looks like you may also need toeboards. I came across these on this site:
http://directsheetmetal.com/Store/in...roducts_id=219
They are great and reasonably priced. Very solid. Here are a few pics starting on post #34.
http://6066gmcclub.com/showthread.php?t=49268&page=4
Good luck!