@Richard Cranium, the trunk mat for the Sport Satellite is factory original to the early production cars. I know of three other early production Plymouth B-Bodies with this style trunk mat. The ones that I know about were all built in mid September to mid October and yours is the earliest one that I have seen. I have never seen the material used in the Dodge's so if someone with a very early Dodge could chime in, that would be great.
Unfortunately, the one in my 68 Road Runner was nothing but pieces as it was an ex moonshine car from here in Georgia and saw a rough life. Keith Rohm had a very original 68 GTX with this style trunk mat and as I recall, it was also in the 13,000 mile range when he had it. I think it went to Frank Badalason, but over the years, have lost touch with it.
The material is know as Burtex and was quite common back in the day. It was still available for a number of years, but it did not offer the durability of the rubber mats and thus Chrysler and the other manufacturers moved over to the rubber and carpet mats later on through the years.
Great time capsule for us to learn from, take care of it!!
Richard