I don't know if it had ever been messed with but my 67 had the carpet directly glued to the metal panel. Looked like they just lined the outside of it with spray adhesive and then made a few S patterns with it in the center and that was that.
Personally if I was doing it myself, I'd put some sound deadening on the floor below it or at least under the carpet. Couldn't hurt unless you're doing a 100% factory restoration. It's not like anyone would ever know it was under there.
