Complex sentence: As with the Marathon, the HPR-3 Herald was originally configured with four Alvis Leonides Major piston engines of 870 hp (650 kW) each, driving three-bladed propellors.
Split into simpler sentences: As with the Marathon, the HPR-3 Herald was originally configured with four piston engines. In the case of the Herald they were Alvis Leonides Major piston engines of 870 hp (650 kW) each, driving three-bladed propellors.