I've added a couple of leaves to my 68 road runner and I didn't use anything between them. So far I haven't had any ill effects. I know the fabric you are talking about. The 65 Fury I had used the same stuff. I guess it was to keep down squeaks and/or to keep the leaves from wearing into each other. I don't have a clue what it is or where you'd find it. I know later they used plastic between the leaves. Good luck!