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.
yes, the frame horns are different, they can be cut off, swapped and welded. there's also a cowl to fender mount bolt that's different, it can be worked either of 2 ways; add the mount point to the cowl or swap the inner fender brace from the later fenders to the 72 fenders. while it does seem like a lot of work the swap is very popular.
Glad to see those pics on the other thread you posted grclark. I forgot uys use to put Edsel front clips on the 58 and 57 Rancheros.
Seening the 72 Montego Gt clip fitted on a 79 Ranchero with the thinner bumper should help with a visual.