Perplexed, I am just so interested in these types of issues. I've seen a lot of info on these boards on nutritional and essential fatty acid interventions - I'm one of the believers. Love, love, love me a good OT also!
DS#2 is like yours you are posting on. The best support I've found for him has been allowing him to dictate his responses and writing - his oral language (both recep & expressive) are gifted, his written language about an 88. Handwriting, reversals, slow processing speed. He'll give these *great* oral responses ("Since the dawn of time blah blah blah whatever" and then when I tell him to write exactly what he just said, I'll come back to find "Oxygen is good.") Another strategy that has worked is to have him edit his own work for only ONE thing at a time - e.g. now check your spelling, now recheck for punctuation. Ugh, this is so time intensive for him.
For this summer's "home school," I've gotten him both the Language Mechanic and the Punctuation Puzzler workbooks from the Critical Thinking Company. They really look good-love, love, love their stuff. I am also going to have him work with a tutor on composition. I got a book of court cases from CTC, "You Decide" or something, and we are going to have him write decisions. He wants to be a judge. His problems with punctuation have really challenged ME - how can you not "get" apostrophes? Why would you have to cover their use more than just the introduction to them??
Also, my DS doesn't have the "H". I took him for a central auditory processing evaluation at 2nd grade (he's going into 7th) when his teachers said attention problems. He does have problems with background noise that have lead him to the habit of just tuning out. This is the basis of his 504. He still is a bit below where we'd like him in looking people in the face and speaking to them, e.g. coaches. Engage, son, engage!!
Lastly let me say with the mixed dominance, he's a really good batter. He's left eye, right hand and that gives him a split second advantage. Thank goodness he gets to USE the advantage, and not just the academic challenge. I really keep him in sports for the coordination etc. Also, and I think relatedly, they did find he is gifted in creativity. Now just how do you program for that?! They had no answers.