[67mater]

If you are doing a full floor, and doors fit with decent gaps before, I would start by welding square tubing across the door openings and diagonally from corner to corner, inside the cab so door could be tested fitted while bracing still in place. Also measure between rockers at front middle and back to see how that compares to new floor; too narrow is an issue.

Did you have a plan for supporting cab while you cut the main floor out? Once supported, I would cut the floor as comfortably close to front and back seams as possible and then drill out and peal back the factory seams. You will also need to separate the main floor supports that run front back. I would then trim or bend the bottom of the outer rockers and replacement corners enough that new floor can come in from the bottom. It should be able to be centered and clamped all through the middle on the front and back walls.

trim/bend/modify prep as needed and then I would go ahead and remove old rockers and old corners fully and test fit A pillar bottoms and kick panel bottoms (if you need replacement) along with outer rockers and b pillar bottoms (again as needed). the cab corners can be the trickiest, but Id' recommend the doors be reinstalled and everything double checked to fitment back on the frame so you can be see the body line curve match up. I personally think staying below the body line is better for the corner seam, but since yours were overlaid, you'll have to decide.