The booster would achieve liftoff via five regular F-1 engines; four of the five engines on the Saturn V-B would be jettisoned and could be fully recoverable, with the sustainer stage on the rocket continuing the flight into orbit.
The booster would take off using five standard F-1 engines; four of the five F-1 engines on the Saturn V-B would be discarded and could be fully recoverable, with the sustainer stage on the rocket continuing the flight into orbit.