PDR,
Re MRA 4, off-the-shelf commercial EFIS were selected; well proven and a European supplier. The FMS was similar, UK manufacturer of a proven operating system and known aircraft interface.
However, it isn't easy to interface an Airbus tailored EFIS and a Boeing biased FMS, and expect a split dual system (flight deck and cabin) to work in the same way as an airliner. So then you need three CDUs and another EFIS display to handle the 'cobbled' aircraft systems and the additional tactical requirement ... ... then you are surprised that it doesn't fit within the older style of flight deck geometry.