I am absolutely no expert, but I do have a 10 year old with High Functioning Autism. A lot of your grandson's traits, my son has too. It's frustrating for both of us as he is extremely smart, but extremely disorganized in thought. Counseling has helped him, as has group therapy with other autistic kids. The right kind of counseling has provided him with tools and coping strategies he can use during difficult situations for him. As he moves to the higher grades, with more homework demands, and more abstract learning required, it's been more challenging. We are considering looking into medication, as it does help a lot of others with these issue to focus better.
I think you should look to the Autism Society for testing centers and have your grandson tested. It's likely a free test, and will last all day. Autism is a spectrum and all people have different severities, so there is not "one approach" that will work, so the counselors at the testing center will be able to help with a recommended therapy program.
One thing with my son is that he tends to use his autism as an excuse why he can't perform the way someone else can. I try to discourage that, and as a result he's really come to have some confidence in himself that even given his obstacles, he's able to succeed. It's certainly a daily struggle for all, but if you can keep his mind on the course of "I'm going to fight this even harder!" rather than, "I'm destined to fail so why try" that will be huge for him! I believe the Autism Society can help with job placement too, if I recall.
Good luck!! I hope your grandson finds some answers because he sounds like he has so much potential!