Human Factor,
Our bunks are in a small cubicle just aft of the f/d, on the port side. The door opens outward to block the corridor from the forward galley, thus leaving a Heath-Robinson affair whereby you can get changed between the galley and the f/d entrance door. The bunks are tiny and, just like the -400, your head is lower than your feet in cruise attitude. It is quieter, however.
The cabin crew have a bunk-room just aft of the mid-coach galley.
Our longest sector is JFK-NRT, approx. 14.30 in winter...
Good luck with the retro-fit. (I've got former RAF-mates flying your 777's...)