Russ,
I am not an expert on this. Mine as a preL has a keyhole shaped slot in the male end of the lap belt. This would be where the separate shoulder belt attaches. On Ls the shoulder belt hung in the same attaching point on the bulkhead (with a retractor) and was sewn on to the male lap belt.
I think that you would have to swap out your lap belts to make this work.
Jeff
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