had the spare tire inside because the battery was in the trunk where the tire was supposed to be. For '66 the seat became an option ( that most cars got) and the "package tray design changed to a shorter "ribbed" version. I have one of them in my '66 GT350 for the weight savings and the original back seat is safely stored for the next owner to deal with.
The picture in the above post of the business coupe is how "I" would do the Falcon if I had it. Nice , clean , simple. It could be done with vynil covered aluminum on the back and vynil covered thin plywood on the bottom in case you needed to carry anything back there.