micasb - That was indeed the story I was trying to demonstrate through the medium of emoticons!
locost47 - Yes, the difference in disc radius (i.e. 144mm to 172.5mm) should largely be taken up by the lugs on the carrier. More precisely, the distance from the mounting hole to the top of the pad inside the caliper. I don't have the two different calipers off the car to measure, but since the caliper/disc combo don't fit my hub carrier, measuring them won't help them fit. I have wondered about having the diameter of the discs machined down enough for them to fit inside the calipers.