I'm glad to hear your ds has taken off now in his reading and overall also in his writing! Do take time to celebrate that, as you have been at the helm of all that and have really overseen and encouraged that excellent growth!!!
In regard to helping ds with his spelling, I would have him do daily dictation, using maybe levels 7 and 8, or starting with 6 if that seems a better fit. I'd have him do dictation each day, and I do think you will see some growth, even if this is just for a few years.
My ds had speech therapy and struggled with spelling early on - dictation has done wonders for him. I think you will still see improvement, even if it is just a few years' worth of dictation.
I would also correct all your ds's spelling within his writing as soon as possible. Ideally, you'd sit by him with a markerboard and have him erase and rewrite misspelled words as soon as possible, looking at your model written correctly in black on a white markerboard. However, the ideal is tough to pull off sometimes, at least for me. If you are near your ds while he is writing, and he wants to know the spelling of difficult words, that is fine for him to ask you. Have a markerboard near, and jot the word he is asking for help for in black on the white markerboard. Or, if you are not near while ds is writing, when your ds hands in his work, I'd immediately have him fix his spelling. You can either jot the correct spelling in the margin of the line the word is misspelled in, write it on a sticky note stuck next to the line he misspelled the word in, or lightly underline the misspelled words and write the correct spelling on a markerboard in black for him to fix. The key is for him to begin to see over and over the right way to spell words he is misspelling, and for him to as quickly as possible erase the incorrect way he spells things - hopefully beginning to help him see when words 'look right' and when they 'look wrong.' It won't help to spell the words out loud for him, as this isn't helping him see it written properly. He can use spellcheck if he types some of his work as well. This is a tool many adults utilize, and it will be a help to him as well. I do think you will begin to see some progress this way! HTH!
In Christ,
Julie