I would strongly recommend against any "major" parts replacement with the cab off the frame. Your frame is like a fixture and since that's where the cab will wind up in the end it's a LOT better to know it will fit when you're finished cutting and welding than to find out the hard way when you try to put it back on after working on it off the frame. When you get it all welded back together and you know your doors fit with it on the frame THEN pull it off and put it on the dolly for cleaning and painting.
I never took mine off the frame. Even when I was done with the surgery part I just rolled it back on the frame to get access to the bottom. For pix, start
HERE and hit the NEXT button a few times to see what I did.
There was a guy here some time ago who did it off the frame and he had some major horror stories to tell.
