Was reading an old post of yours and you mentioned your boy (last summer) hit 75mph as a 6'2" seventh grader. Now you are saying that he is throwing 83-84 as a 6'3" eigth grader? Personally I have no advice to give you. I should be asking for advice from you. What program are you on that increases velocity 9 mph in 6 months? Not that I think it is impossible for a 13-14 year old, just extremely rare!
If he really is throwing mid 80's now I would start shopping for the best coach in the country, get him to try out for the national USA Baseball team and get him into the best of the best showcases possible. In my area I live in which has some of the best competetive talent in the country for its age, most seventh- eighth graders on travel teams throw mid 70's with a few (less than 5) throwing close to 80. We had one kid last year who made it to the final cut of the USA Baseball team. He threw high seventies at that time maybe even topping 80 on occasion. Mid 80's for an eighth grader is exceptional talent and probably only a handful of kids in the entire country throw that fast at that age.