i'll be able to book online 12 hours pre-flight, but obviously have to do it seperately for each flight.
im not bothered for teh LHR transfer, only the international.
i presume, like you say, that the exit seats wont appear on the online-checkin area, but will the seats with extra room that are not next to an exit be on there? ive heard that on 747 400s there are seats near 'bulkheads' or somehting, with added room.
last time i was on a 747 i wasnt aware of such seats and so didnt look to see what they're like.