[68bowtie]

put the header panel on first so while you put the sides on you have the panel there to help support the sides. the header panel goes under the floor. the bedsides can only go on top of the floor.

i haven't re-assembled one myself so the rest of this is just speculation, but i would put the wheel wells on next. everything else at this point would be loosely bolted with a few bolts til i could square up everything and tack weld the rear brace. i wonder myself how guys make sure the distance between the bedsides is correct (do they mock up the tailgate prior to tack welding). hopefully others will chime in with better info. that's just my .02...