After fitting the bulkhead carpet, the harness bolt holes were covered and needed to be cleared using a scalpel. The Harness shoulder straps are then secured into the cross rail - but need to pass through the strip at the front of the Boot Cover. This strip has an aluminium bar inside to provide some rigidity and is predrilled with holes for the harness bolts.
The fixing stack starts with a washer above the Harness plate, a crinkle washer and top hat underneath. In this configuration, when the bolt is torqued up it exerts pressure through the harness plate onto the top hat, and the crinkle washer provides a little friction to the harness plate but allows it to rotate.
When I tried to fit the Harness straps two issues came to light: (1) the holes in the Boot Cover did not exactly align with the holes in the chassis and (2) the left most Harness bolt would foul on the Track Day Roll Bar cross strut. Both of these issues made it impossible to fit the Harness bolts.
Fixing stack ; bolt passing through Boot Cover, but out of alignment with the tapped hole in the chassis
With all other bolts removed, I managed to get the left most bolt in position under the Roll Bar. The right hand hole in the Boot Cover strip then needed to be filed to remove about 2mm of material to allow the Harness bolt to pass through. After that, the fitting of the harness shoulder lap straps was straight forward.