Depends a little bit on what kind of meeting it is - how long is it, and is it you and your son together, or just you? If it's a long meeting without your son, I think I'd assume they really want to know, and turn up prepared to discuss the lot. If not, I think I'd keep it very low key. Are you prepared to give the teacher a copy of the WJ-III results (or the front page/headline scores, or whatever), and will they be reasonably comprehensible, e.g. will she see that they say his spelling is at the level of an 11y4m-old child? If so, the easiest thing might be to hand over a copy and say something like, "I don't know how school's going to go for him, but these test results are saying that he's very unusual, so I thought I should share them with you. Maybe we could set up another meeting for a couple of weeks after term starts, once he's had a chance to start to settle in and you've started to get to know him."
I think you have two things to avoid, Scylla and Charybdis style: saying too much, since that amounts to having a conversation now that will be 1000 times easier once the teacher has got to know your child; and saying too little, since if you "drop the teacher in it" i.e. you have a chance to warn her that she's getting a wildly out there child and you don't take the chance, it may come across as having not helped her to have time to prepare when you could have done.
That said, he's entering early, so she must have been told something, I'd think. You may find she'll be asking lots of questions and it won't be an issue.
Does he still have noise sensitivities etc. that she'll need to know about? If so, that might be more important to spend time on, since she can hardly miss the academics but you'll want to ensure that he doesn't just get labelled "immature" if he finds something hard to deal with.
Overall, I suggest, err on the side of saying too little rather than too much, but go in with the assumption that you're meeting a good teacher who's going to get to know him and do great things and that you're going to be able to trust that he's in good hands... Here's hoping that's true!
