I think the 1-tons had a heavier bumper. Both of my 1-ton panels have a bumper that is the same style as the regular AD bumper, but is thicker than the one on my 3/4-ton parts pickup.
Too bad the medium-duty Chevy bumper doesn't look like it will interchange with the GMC. I'd move the 4400's over to the 350. That 350 bumper looks like it's about twice as thick as the Chevy version, though. GMC engineering strikes again...
