Those units and components are remotely installed and connected to the engine by a drive shaft that drives multiple types of accessories. Does not include those accessory drives which are bolted to and are immediately adjacent to the engine.
That portion of the system is used to conduct power from the engine to the gearbox. Includes items such as drive shaft, adapters, seals, etc.
The case contains the gear trains and shafts. Includes items such as gears, shafts, seals, oil pumps, coolers, etc.