This sort of thing varies alot depending on which state you are in, which engineer you are using and who you know. You've taken the right step of talking to an engineer to get your facts straight.
And as for the diff coming from the Jap version of the car, that really doesn't matter, it never came in a Sprinter in AUSTRALIA, so they have no evidence it is safe for Australia. Can I bring some old Trabants over from the former USSR and claim "but they were legal over there" when I get reamed?
Hen