MAN to MCO time change and aircraft change

Got a text from virgin to say they have change our flight times for August 2012 from MAN to MCO and home again, this doesnt bother me as its only by half an hour or so. However i did ring virgin atlantic as i now cannot access my seat for the return trip (VS076),the lady said its because we are now flying back on a 747 instead of a A330 and they wont be sure which config it will be due to the referbs. She reasured me we would be flying out on a A330(VS075) still, which im glad about because ive been looking forward to trying it out!!! I just hope we are lucky and get a shiny new 747 home. I do wonder why they are flying 2 747s back now instead of just the one. Anyone got info?