Dart/Duster Bumper ?
You got shock mounts or brackets on the 74? You can put a 70-72 Duster/Demon bumper on the rear. Will need to find a way to mount the brackets if your car had shock mounts. There will be a big hole that the shock came through that will need filled in with some sheet metal. Then some holes drilled.
If your 74 has brackets I am not sure if they are the same or not as the 70-72 brackets but again worst case is you will have to drill a few holes. Then run bolts with nuts or weld the nuts on the the bumper mount panel.
Here is a pic of me holding up a glass 70-72 bumper on my 75 Duster. As you can see there is no lip on the ends of the later cars 1/4's to hide the bumper gap there. Need to either weld in a lip. Or if a glass bumper is used maybe graft some more glass on the bumper in that area. Or just say F it and have a gap there. :D