The carpet is glued to the sheet metal panel that comes out to expose the spheres. Held down by two screws beside the rear seat bottom and, I think, two screws in the carpet itself. Could be wrong there. May also be a screw in the center of the third seat, too.
The panel will be stuck down pretty good, be carefull removing it not to bend it. Covers the whole area between the second and third seat.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!