As for the reason of moving the filler from the back to the sides, I'm going to have to go with safety, though I don't know if that's true. I'm assuming the whole drop in gas tank in the trunk is why it was in the back?
Here's an actual picture of the hinged light in a 52 Cadillac.
http://oldcarandtruckpictures.com/Ca...ler_detail.jpg