S.H.
It sounds like you really want to do what is best for your child and I commend you for that. I'd be pretty upset if I were you and I would like to hope that I could approach it with the grace you're showing in your post!
Without knowing more about your ex's request and how he's approached it, or where on the A spectrum your son falls, it's hard to understand what the best course of action would be, but here are my reactions:
I would talk with your ex (I'm having such a hard time typing "Father" in relation to someone who has not had a relationship with his son for 9 years.) and evaluate what kind of relationship would be best for your son. Then you lay down very specific ground rules and say, "You're asking a lot. If you want to do this then you will have to do it in a way that is not harmful for your son. You will stick to a routine and never ever break it. If you do, the deal is off because there is no chance in hell I'm going to give you a way into his life and allow you to hurt him. Then lay it out, when and how often he has to call, when and how often HE can fly down to see your son, when and how often he can bring his family and how they will be introduced. Let him know that this will not be done on your ex's schedule, but your son's. If things go well over the next few years you will think about allowing your son to visit him in his home.
Or if you think it's really not good for your son, I'd say, "You have made choices to not be involved in your son's life and now it is too late. You are welcome to write me for updates and I'll send you photos but the sad truth is that while you have made choices, my son has not. Through no fault of his own, he had no father in his life. He doesn't care at this point, and I will not create a situation in which he starts to care, only to feel let down in the future or hurt that you did not care for him in all these years. As long as you remain off his mind, he doesn't live with that pain. He does not know you and you do not know the first thing about him. If you did, you would know that this relationship at this point in his life would be more difficult than good for him. I hope you understand that he is not the same as other kids in many ways. He has special challenges and special gifts. He will not relate to you in the way you would like and your sudden appearance in his life would not be a positive experience for him."
I would record all conversations with him, too. I don't know about the law where you live, but in TX only one party has to know that the call is being recorded in order for it to be admissable as evidence in a custody hearing.
You've gone at it alone for this long. He doesn't have "rights" as far as I'm concerned (and I'm not the law) but your son has rights, needs and wants that his "father" needs to bow to.
Good luck to you.