Dan interesting find and puzzle. In the pictures you provided we can see the (first two top pictures) the panel that is in question and then a picture of a typical waffle style insulation panel for the sport roof package tray for a non fold down car and finally the package tray for the same. So from scaling the question panel to the tail gate and the package tray it is not as tall nor as wide and the package tray or the typical insulation panel plus has a couple of addition cut outs on one edge and lacks another on the other long edge.
I think that Mike is correct in that it is a divider panel that would be installed between the rear seat of a coupe and the metal panels/reinforcements that lead into the trunk and attach to the metal package tray panel. Spent a while with this chasing down possibilities and facts
I rotated the one picture to show the orientation (likely IMHO) it if installed in a car with a non-moveable rear seat.
If you notice there are two (arrows) cut outs for securing the panel in place which once opened would slip over a horn sort of section of two of the panels between the interior and trunk of a car.
If it had been from or repurposed on the factory line from another car built on the same line we have three main issues
First - the material is not the type or from the same provider of the typical style used at any of the three plants in 70 for this purpose. Only two style I've been able to find at all of the plants is a limp uncoated jute underlayment layer either very dark or a medium brown. Both held up poorly over time
Second - the orientation of the knock outs and the cut out for the seat hooks are reversed on the part in question
Third - the design does not match what was used on other cars on that same line.
On a 70 coupe application there were four spots for knock outs to attach the panel and hold it in place. Two upper and two lower. Since Dan's panel in question only has two that should eliminate that possibility
If your still trying things to figure this out you might want to compare the different pattern pressed into or the dust pattern in the panel to the metal reinforcement panel to see how it lines up.
Since neither of the two knockouts were used IMHO this panel was originally installed in a fastback as a makeshift insulator panel for some unknown reason. What it was originally designed for I don't know and one would need to search all the other Ford and Mercury body styles built that year. Likely only a handful of spot roofs were built with this insulation panels at a specific plant and time period. Since we don't know when or where this came from I would not reuse if for that purpose but maybe used the material for making a bunch of under the rear window panel insulation that is visible through the trunks on 69 and 70 sport roofs
Best I've got at this point.
