C Cubed Aerospace offers passenger to freighter conversions for the Airbus A320 and A321. These freighter aircraft provide many advantages over the entire Boeing narrow body family: 737-300, 737-400, 737-700, 737-800 and 757-200:
More containerized cargo volume on both the main cargo deck and the lower cargo deck, with cargo loading systems
More modern aircraft design architecture
Lower direct operating costs
History has proved that freighter conversions that offer additional cargo volume become the dominant choice when considering a freighter conversion.