We are flying from SFO direct to HND. Unfortunately by the time the equipment change was announced, the rear 2 seaters were already occupied

Do you mean Y T-48 as in booking class Y, 48 hours from departure? Unfortunately our flight is also not even in Y class, we are in L.
I guess our best bet then is probably to just change to the center aisle seats D-E for the best chance of being undisturbed.