Do keep checking for changes, but I would not be terribly optimistic. We are also flying BA 48 in May and the upper deck is completely booked. This may be true of many May flights---as people realize this is their last chance to fly the UD on this route. (The 747 is being replaced with a 777 as of June 1).

If nothing opens up, think carefully before asking someone to move. 63B may appear to be perfectly equivalent to 63J, but perhaps the person in that seat has a companion across the aisle, so won't want to move. If both people (63 A and J) decline your request, then you and your wife will end up seated next to these same people. Not entirely comfortable, in my view.