71-72 duster hood for a dart
but I have no idea where to start
No idea? How about posting some pictures like SEVERAL people have suggested. This would clear up probably everything.
ALL 73-76 Darts came with this style front end:
If yours does not have this style, someone swapped parts on it. THIS is why pictures help. You are clearly not experienced enough to know how to describe what you have which is why pictures would go a LONG way toward helping you.
Personally, I have several 70-72 Duster hoods, a 72 Dart hood, a few 73-76 hood and even 73-76 Duster hoods.
You are making it impossible to help you.