Problem with four doors is that they are not as popular today as they were when they were new. Back then fewer wanted a two door than did those who wanted a four door for family transportation. Today everyone wants a two door (usually a smaller sportier than an Impala but some like big cars as well and they still want a two door. That means that even though the Impala isn't as popular as the smaller cars (Camaros and Chevelles) there are fewer reproduced parts for a full size four door than any other car of this era. You will most likely have to scrounge flea-Bay or Craig's friends for a used part for sale.