MM,
You might find Airpower's comments
here of some interest.
Also, Boeing says (Jackonicko notwithstanding) that they are the good guys on MRA4, see page 17 of
this document...
And while there are a few 1960s bits and pieces in the P-8A, the 737's been through a couple of major overhauls since then; and it's not just the age of the design, but the fact that there are 5000 of them flying around.
I'll leave the doubts about twin engines to the professionals except for pointing out that today's engines are far more reliable than the engines of the 1960s... and that the US Navy is no doubt glad that it passed up BAE's proposal to sell them MRA4s for MMA.