Just a suggestion: what about not using the word gifted, but sharing scores, in context (i.e., percentile and what that means, how infrequent, yes, even in that area, such IQ scores are...). Given the school system has absolutely no gifted anything, I'm going out on a limb to say they know, well, not much about gifted learners. You could share documents about the concept of asynchrony and how that can be expressed in a classroom (your DYS contact should be able to assist in supplying some of these). Ask how they can help him, given his ability profile and his other differences.
You might say something like "we've been hesitant to share this information, because we get the impression that asking for something based on it isn't often taken well. We don't want to be "those parents," but we do want to share what we know objectively, based on expert assessments, about our son."
I see where you are coming from, but at least in our experience, it's pretty hard to separate the PG-ness fully from everything else. Keep in mind that your son is both Es. It is only reasonable that the school has some information about both, otherwise, you are only sharing part of the story with them.
Since you mention becoming braver, may I share two thoughts with you? One is something a friend told me when I was pregnant with ODS. She said she had realized during a doctor's appointment where she didn't feel concerns were being addressed that if she didn't advocate for her daughter, absolutely no one else would. That has stuck with me and guides me as a parent.
The other is a book I'm currently listening to called "Playing Big," by Tara Mohr. Very empowering for some of us who have confused criticism with reality or let it stop us, among other things. Only speaking for myself, of course. YMMV. :-)
