I feel for you and your DC, Pinecroft. While I don't have personal experiences of this kind in my own children, on the professional end, I have met and worked with many, many children who experienced physical symptoms when in psychological distress (aka, somatization). And it's specifically not uncommon for GT kids with poor instructional match to report stomachaches or headaches.
On some level, it's not immediately important (although ultimately it will help in the process of developing solutions) where the stress points are; it's more important simply to recognize and acknowledge to him that they exist, and that caring adults (parents and others) see his pain, and are taking steps to create supports and solutions, even if it might take a while to figure out. And more than likely (as you note), it's not really just one thing, even if he's only verbalizing symptoms in certain domains. Of course, he is giving you some starting points to investigate.
