Aw that little love!
Have you talked to the schools senco about any turn taking activities they can implement as part of his daily routine?
My own son does music therapy where in the small group they take out of the class they practice taking turns with beats and claps, as well as songs and rhymes and they set him small goals at first like waiting 30 seconds, then 2 minutes, then 5 minutes and so on. This has really helped him with the delaying gratification issues he struggled with previously.
It's also really helped him have a circle of friends, because it has been adult organised play based education so the other children have seen his development and the modelled behaviour by other adults to replicate. Things like "stand back please" and "can I have some space please".
It sounds like he's got a really strong sense of justice too, and might need help regulating his emotions but might not be developmentally ready to understand the premise of "do you want to be right, or do you want to be happy".
Our school has got a social, communication and interaction worker that comes and reviews his SCI plan every few months, and they're really good at putting the foundation steps down in a way that's motivational to your child. It might just be that they have to schedule time in the day to talk about what's worrying him, or give him a card to give to a teacher when he needs to have some worry time to air off at an adult who can then manage some coregulation techniques with him.
I hope they can implement something for him. He sounds lovely, just very misunderstood and highly deserving of friends.