The rear end of a Bronco step is attached exacly like the front of all steps; a U-clip/bridge bonded to the fiberglass step face, and bolted to an L bracket (F2T3-16C078-AB front; F4TZ16488A rear), attached by the wheelwell screw. F-series bolt a bonded clip directly to the cab.
UPDATE: As of 2023, I have the small front & rear L brackets that connect the ends of the fiberglass steps to the body, and the bridges glued to the steps' ends for sale.