Looking towards the end of the year, all the 747 flights look NBC equipped. The 255/254 combinations has recently been operating with OBC 74B. Hopefully by the time you travel there should be little risk of that. FWIW I far prefer the 747 in J and would try and avoid the 343.

Either of the evening flights from LHR is good (i've never really noticed any difference in the catering between the 2. I hate the day flight as it seems designed to maximise jet lag. Coming back from HKG, the earlier flight (251) is preferrable as taking the 00:45 flight makes for a loooong night. There is a boiled dinner serivce once you board so it can be difficult to get any sleep before about 3am!

Also, the 251 typically has heavier bookings so there is more chance of an upgrade!