Dont make it sound like you have to do alot to make a 68-72 door fit a 73-74 they fit right on and open and shut just like they sould the only diff. Is 73,74 didnt have vent windows. And with that being said its as easy as pulling the pins and changing them i know because i have a yard full of 68-74 novas and ive changed them around to see if they will fit. And the door latches are the same on all of those years.You said doors and I was thinking floors for some strange reason.
The door skins interchange but there were changes to the doors themselves for side beam impact and the ventilation (deletion of vent windows). The mirrors were also different in how the attached but that is a minor modification. Door latches also changed as did the locking mechanism which means the inner doors are different over the years but the latches could be upgraded to the newer style and no one but a concours judge would be any the wiser.