SID isn't in the DSM, and Childfind rarely if ever actually gives an actual diagnosis. They do recommend strategies/therapies where they see an educational impact. So I would really make sure you have all the facts.
Secondly, I've known several families with kids on the spectrum who swear by a GF diet. However, there's no clinical evidence to support this. It can be a bit of hassle but if you see behavioral improvements, then it would be worth the effort.