I would take the middle block of seats and park yourselves on both aisles. Those middle seats will be the last to fill up . If they do, then you or your friend can just swap one aisle for one of the middles and sit next to each other.

It worked for me.....except someone nice blocked the middles for me and there was a stranger on the other aisle.

If I am travelling in Y on a 747, I do prefer the middle block over the window seats, only because if it is a full flight, at least only one person climbs over you in the aisle to get out. In the window section, you have 2 people climbing over you, if you are in the aisle seat.

Good luck.