The reason you need to remove the rear seat (cushion and seat back) is to gain access to the top of the shocks.
The seat back is held in by 10 mm bolts in the center and two outboard areas, left and right. The seat back is removed by lifting straight up. Be careful when removing it from the car because the lower "arms" can VERY easily scratch paint.
Once the seat back is removed you will need to remove an insulation pad (easy). Then you will notice two white plastic covers. Pry them off and you will see the top of the shocks. In order to remove the shock you will need to remove the two nuts. Sorry I am not sure but I think they are 14 mm. Since the second (lower nut) will want to turn with the shock, you will need to use a small crescent wrench or other tool to hold the shock shaft at the top.
Once this is done go to the bottoms. It is much easier to do this by jacking the car up. The lower portion of the shock is held in place by one bolt.
Installation is simply in the reverse order.
Hope this helps.
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'65 911 Coupe (#302580)