My '74 had the fixed portion of the long shoulder belt on the steel rocker plate, which went up through an eye attached to the rear bulkhead bolt (shoudl height) and down to the inertia reel which was then located behind the rear bulkhead panel. The bulkhead panel had small cut outs in the bottom that a cover plate screwed over the top of.
Much like David's later GT5 except the inertia reel was hidden behind the rear bulkhead panel and the fixed mount went through the rocker plate.
Do you have a mounting point behind the bulkhead cover?
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