For the IAS, a 131 IQ is plenty sufficient. So... you might think about using that as a compromise issue. Go in saying you want to use the 144 GAI, but show how willing you are to work with them by accepting the 131 to be used for the IAS. Then if there is another borderline decision, point out how you gave in on the IQ score.
I would highly recommend buying (or borrowing) an IAS manual. There are lots of questions on it which you may want to have thought through your answers for. The school will likely try to dicker with you on some of them, so be prepared for a give and take game. But if you know what questions are coming, and how many gives you can live with while still getting a good score, you can make this process work.
Having even one other person in the room on your side can be huge, so if the psychologist is able to come, I'd seriously think about asking him.
Best of luck,
--S.F.
