Thanks all...
MMB doesn't have 3 E or F blocked, which I believe would be SOP for a bassinette location.
No problems re length of service in WT+ as we've booked the return on a daylight flight via BOS, but the point about the seatbelt sign is understood. Those North Atlantic flights don't tend to be too bad - it's the flight to SIN in a couple of months that i'm worried about - across the Himalayas then the bay of Bengal - will be lucky if the seatbelt sign is ever off...
(No problem for you guys though, as we're booked with the nice folks over at SQ for that one

)