there are many red flags in your post.
if you are looking for a large dog (80-90lbs) that is truly game. then you are not in the market for a pit bull. the further you go beyond 45lbs, the further you go from a properly bred American Pit Bull Terrier. those 120lbs monsters you see on youtube ARE NOT pit bulls.
there are a few bloodlines that are typically larger (60-70lbs). but i get the feeling you are looking for a really big dog.
there are people here with alot of knowledge about game dogs. if you describe the purpose and function of the dog, like protection of farmland or livestock, i'm sure someone will suggest a proper breed of dog.
no matter what function the dog will serve, a breed of dog has already been created to fulfill that role. there is no need to create a new one.
~ jo and Gotti Boi (aka Thunder Thighs, aka Jughead, aka The Doo Doo Monster, aka Sexual Chocolate, aka Mister Smiley, aka Sofa King)