Way late to the party about the carpet with plastic backing. My experience with dealing directly with AAC for the carpet in my Chevelle was, they were very willing to work with a person to get what they wanted and may well be willing to leave that backing off for future people looking for that option.
As far as I know, the Dark Copper color carpet I have in my '66 was never offered by Chevrolet and possibly not any GM car, but ACC makes these on site and offer ANY of their available colors to be pressed and cut to the vehicle it is intended for.
Always worth a call to inquire about modifications...
