Craig
I fear you may be heading up a blind alley with these weight and balance figures. They are immensely important with regards to straight and level flight, but I have to question their relevance during the break up sequence.
Contact with the embankment removed several outboard feet of the starboard wing. Initial contact with level ground appears to have removed the nose and in all likelyhood most of the remainder of the starboard wing if the bank angle was actually around 90°, which of course you dispute.
This means that the remains of the aircraft would be very asymmetric, making a nonsense of any calculations based on all or part of an intact airframe.
It is necessary to start somewhere with the calculations, but I think this will be a much more complex matter than just considering a change in the centre of gravity caused by the loss of parts of the aircraft. I do not consider this can be a valid aproach to modelling the final disposition of the rear fuselage and wing box section unless it can be worked out for varying degrees of bank from level flight to at least 90° of bank. 10° increments would suffice to show the broad distribution of wreckage resulting and may contribute towards establishing exactly at what angle of bank the aircraft struck the ground. That is to say, whatever angle of bank calculation best fits the distribution of wreckage actually found at the scene will go some way to providing a definitive answer to whether the aircraft was levelling out or the bank remained completely uncontrollable.