I'm not sure why your dealer is suggesting the ARB's are wrong. My contact confirmed with AG today that those are indeed the correct part numbers. Did they not fit????
Also, I'm a bit confused still around the springs. Are the ones you ordered the M Sport Springs? or M Performance Springs? If the former, then how is the car going to be lower? I'm ignorant when it comes to this, but my understanding is that it's generally the springs that determine the ride height... no?