Premed,
I would go ahead and use the MCAT III scale given that the 480 series exams were made during that time (from what I've heard at the PR). I believe the A-D exams also use the MCAT III scale, but they inform you to use caution when grading the sciences since those exams have much more difficult science question than the real MCAT. In any case, the 480 exams are pretty good, but the published AAMC Diagnostic Exams are MUCH BETTER indicators on what to expect on the real exam. Good luck with the MCAT in a couple of weeks.