seatguru is useless (at least for BA), so ignore it.

The best seatmaps are usually to be found at http://www.thebasource.com/seatmaps.html

One would need to know which date you're flying on to check, but on a quick and dirty run through next week (23-29 November inclusive) it looks like on all 5 of the days when BA93 is being operated by a 777, it's a 777-200 of some kind.