cfranklin,
If it were me; I would do it while your cab is off the frame. I had to replace some the floor, most of the cab corners and both rockers on mine and did all of them while the cab was sitting on some old pallets. I did not even attempt this with the cab on the frame. I figured it would easy if the cab was off. You can flip the cab up on it's back and weld the floor panels from the bottom side if needed as well. When you weld the rocker panels in, I would think it would be way easyer to turn the cab up on the side or back so that you can stand upright and weld them in. I am not the welder guy they would like to lay under soemthing to weld.
The floor boards also help support the cab and keep it square, so if your cutting a lot of the floor, make sure to brace the door opens and stuff. One of the guys here had some good photos of his truck while doing a major floor panel repair and I went off how it had done it. I guess that depends on how much floor you cutting out.
When you start working on the rocker panels, I would make some good card board templates of where they are located in reference to the cab corner as well as the front post(where the door hinges go). That way you will have something to go by when you fit the new one up. I did that as well as bolted my door back on for fitting and adjusting before I stuck them into place for good.
All in all, mine was not too bad to do once I got started. I worried about it for several weeks before I got started. I had trouble finding cab corners that were big enough until one of the guys here turned me on the the TABCO body parts. Not sure if your truck needs the cab corners or not, they are usually the first part of these trucks to rot..
Any way, good luck, I hope this helps... Let me know if I can be of any help. I just did this a couple of months back so some of this stuff is still fresh in my mind.
