Thanks so much everyone!
I had noticed the steep shoulder and upright pasterns, like you guys said I kind of thought that was breed related. His withers seem a little more prominent than other hackneys I had seen, but I think that might change as he continues to gain weight and muscle (and age, if he is as I suspect only a 2 year old). I think his croup might flatten out a little more with some weight/conditioning as well, right now while he has been gaining weight great he does still have a bit of prominent hips/tailhead and needs some more weight and muscle on his back end. As mentioned I had only ridden him a handful of times because I was concerned about being too heavy for him, especially at his young age. I need to get his ground training to a point where I can put my son on him lol.
I sure appreciate everyone's opinions, and thanks for the compliments! He's certainly still a work in progress, and definitely a fiery little guy. He's lots of fun!