76 Dart front clip swap?

Your biggest challenge will be the bumpers because the '76 has the "shack absorber" bumper brackets front & rear and '73 & earlier do not. I don't know much about the rear tail panel on the 4 doors. I think some came with the lights in the bumpers. But cutting and welding the parts would be involved.

The front is less of a problem and you'd have to use the whole front clip. It's basically a bolt-on with possibly some wiring changes.The earlier bumper brackets & frame could be modified to work together.