[Dave at Pelican Parts]

The late-model retractors do sit between the back pad and the firewall, right where your second picture shows. The backpad has a hollow in it that allows the retractor to fit; the belt goes up to the upper guide (like yours), then down to the lower mounting point. The part that fits into the buckle is in the middle of that, so when it is buckled the belt comes down across your chest and then back across your lap.

--DD