Complex sentence: The previous Discovery models used a ladder-frame chassis where the engine bay and passenger compartment is built as a monocoque, then mated to a basic ladder-chassis holding the gearbox and suspension.
Split into simpler sentences: The previous Discovery models used a ladder-frame chassis. In the IBF the body, the engine bay and passenger compartment is built as a monocoque, which is mated to a basic ladder-chassis holding the gearbox and suspension.