Two hardpoints under each wing. I think the other three structures are fairings for the flap extension mechanisms. Standard engines would be fine. Without commercial requirement to max out pax and freight the loadings are probably down on those of a standard 737 anyway.
Edit: I see the P8 has extra fuselage fuel tanks and ordinance delivery bay which probably brings weights back up to match standard 737s.
Last Edit: Jul 11, 2013 14:48:36 GMT 12 by hardyakka: Extra info
Boeing will start building 13 more P-8A Poseidons under a $2.04 billion contract awarded on 31 July by the US Navy.
Deliveries from the fourth lot of low-rate initial production will raise the service's total fleet to 37 aircraft by the end of fiscal year 2016.
The USN plans to buy 117 of the 737-800-based maritime patrol and anti-submarine warfare aircraft to replace its current Lockheed P-3C Orions.
Boeing's contract also includes funds to buy long-lead parts to build 16 P-8As in the first lot of full-rate production, which is scheduled for award next year. The company says it has now received firm orders for 37 aircraft from the USN, and delivered 10 of these.