Amy, I’m so sorry about your son’s struggles! That breaks my heart.
Can he type? What if he did his dictations or other (normally) written work on the computer with larger font? I don’t think there’s anything wrong with oral narrations, even into later years. As you said, he will have to learn to compose a paper, but perhaps typing with larger font would work better for him? That’s really the only suggestion I have to offer.
Would some type of occupational or vision therapy be helpful for training his eyes to be still? Our dd is in OT at a local public school once per month. We do the rest of her therapies at home and just go there to check her progress. It’s free through the school.
Does that help at all? Or are these things you’ve already tried?