BOAC Flapsnegative - you appear to have been in the area at the time? Was there any chat on 123 about the ride there? Do you know if the (reported) ?TAM? a/c report of 'fire sighted' was reported on 121, HF or 123?
We were at UN866 at FL370 around the time, the AF was at the UN873, one airway to the east. Neither on 123 or 121 there was talk about the missing airbus, not surprising since the A330 went officially missing only several hours later. We didn't hear a TAM report on floating fire either, but there was some low level ELT-like noise on the 121, but it was so faint and brief that it came over the squelch treshold for just one or two seconds, so it is quite improbable to have originated from an aircraft below.
Also there was a post on blue jets lightning, we didn't notice any discharges from above or below, but the moon was actually quite clear when above the clouds (helpful for reference in manual flight without prim or stby instruments, but not within CB) so that could have prevented sighting of a blue jet.
The top of the clouds we experienced at that time I would estimate at FL400, but in the ITCZ it's nowhere the same, it could easily be much higher nearby.