as far as I know, the passenger doors and windows from the four left-over driving carriages are being used to equip the four being converted, to give them two sets of doors, windows throughout- and possibly the seats are being used too?
I'm not entirely sure, but I think the motor bogies may be getting fitted to trailer carriages as required?
With all that removed, you've bascially got four shells. I'd imagine if there's any sense the remaining useable parts will be stripped down and potentially a body shell retained in case of crash damage.