69 Dart Rear onto a 73 Dart
just find and buy a 69 dart if that is what you want.
It would be a major surgery to convert a 73 to a 69.
you could make a 73 look like a 70/71 - with just changing the front end and markers because the rear bumper is the same.
you could make a 73 look like a 72 with simply changing the front end because the markers are the same
However you still have the 73+ interior
74 started the body mounted tail lights and they were not in the bumper anymore so completely different animal.
if you wanted to "make" a 69 dart you would be best starting out with a 67 or 68.
But again ...I ask WHY!!! I would just leave a 73 or 74 as it is because, painted up nice and with a good driveline combo, it could be just as sweet as any earlier model.