I think you could bolt them on. for sheetmetal wise. The body lines at the doors and fenders are the same.
The problem could be the bumpers. The 72 has a narrower bumper and it is molded to the contour of the header and grill, where the 76 is a much straighter bumper. The 2nd problem with the bumpers is the mounting. The 72 has mounting brackets and arms. Where the 76 has rebar bumpers with those collapsible bumper shocks that mount to the frame.
To me the only issue would be the bumper areas. Are they able to bolt right on from a 72 frame to a 76.