for the harness, once you remove the current seat, you will need new attachment points either side of the seat and I recommend you get proper FIA approved plates (about 3x3cm) that have to be welded to the car, and bolts to attach the harness. The shoulder straps of the harness can be attached to one of the two bolts retaining the redundant metal bar in the boot, behind the back seat. when you remove the seats, watch out for the electrical connectors etc, as these will affect your front airbags.