Jetex Jim
Even if, interestingly enough, all the MRA4 mission avionics is straight out of Mr Boeing's (much cheaper) effort.
You are correct that the the core of the mission system was developed from a Boeing product,, just not one designed for the MPA role. Significant work has gone into adapting it, not just for the traditional maritime role but as a proper multi-role ISTAR asset. I would not be surprised to find much of what we have done over the years finding its way back into the P8. However, as good as the 737 platform is, if you look closely at the few pieces of info coming out of Boeing/USN wrt P8, you will begin to notice that the trad maritime role is being down played, not least because they have realised that the fatigue life and wing loading will take a huge hit at low level. There is also an issue with time on station, again looking at the scant data available, and assuming it is not wildly inaccurate, then the P8 is probably only going to manage about 7-8 hours sortie duration.