Continued...
Spent a lot of time double and triple checking the measurements. I used clecos at the middle joint to secure the panels together. Then I used some body clamps to hold the rear cut section in place. The total length was within a 1/16" of the original bed.
I tack welded the rear section and relied on the clecos at the middle joint to ensure nothing shifted. Then I moved it to the ground to start installing the floor braces. I just tacked those in for the time being, too.
Put the panels back on the frame and rechecked my measurements and went full steam ahead on the rear section weld. Took my time to ensure I didn't overheat anything.
Put it back on the ground to install the other two braces. Then scuffed the coating and hit all of the bottom with some epoxy primer. I verified the braces all lined up with the bed mounts prior to filling in all of the spot welds. Also sprayed the rear cross sill. I probably took the floor on and off 10 times before I got to primer. It was quite the workout.