Richard sorry that the earlier response was not focused on your specific need so trying again
As for the divider it appears that during your cars time of production a very dark gray/blackish jute style was installed and glued along the top edge to the package tray reinforcement panel below and in front of the rear window.
The jute sheets should still be available from a number of sources but getting one the right color(s) is the difficult thing I think. Not sure of how to address that other than dying (going to get messy) one of the lighter color sheets before or after you cut it to the tight shape.
Looking at my pictures the earlier part of the year appears to use very dark color jute while the later cars has a lighter gray with much more visible individual threads of different colors mixed in. Below is an example from about the same time period as your car
There have been reports and I've seen some packing (as in moving) blankets and even FEMA blankets that are very similar to the texture and make up of these pads
As for underlayment I believe you will find that there were at least two version's used . The thick three layer used under the carpet and rear seat and a single layer like was used on San Jose during some periods, under the carpet, over the rear end floor pan into the forward area of the trunk.
Under the carpet example. Dark version compared to the more typical brown jut center layer we see most often used at all plants and multiple years
Of course on the hidden (once car is fully assembled) so will choose to substitute other products just to replace the thickness and compression of the original material and be done with it. Same goes for the headliner, B pillar and other insulation
