Texaholic2000,
I have Tom's book and I just read about it on page 127-128. I really wish he would have included a couple of pictures on where he was cuting on the back of the cab.
It sounds like he is taking the back of the cab off all the way down to include the rear door jams? I was under the impression it was taken off below the belt line, Just below the windows.
This is definitely a job for a professional who has done this before. I would never attempt this with my limited welding skills.