First off, before you go get a prong collar, many dogs don't need them. Set the harness you described you had aside and go get a choke collar...not a thick one either but one you would use for a medium size dog. When you put it on, make sure it is all the way up under the chin and you have it on so that when he pulls, it closes around his neck. When your dog begins to pull, it will "choke" him and he will soon learn not to pull. We did this with BOTH our pitties and did it with foster pits that were abused with prong collars and were scared of them. I don't have a problem with prongs if they are used correctly, but many people don't know how to properly use them and cause tramatic problems for their pets.
Also, you need to take him to at least basic obedience classes. I always recommend it to pitbull or pitbull mix owners. They will not only help you to teach your dog, but they will teach you how to properly use the training tools available. In my opinion, if you don't have to resort to a prong collar, it is best, although bully breeds are notoriously stubborn and it may come to that. Used as a training tool only and never keep a choke or prong collar on the dog when he isn't on a leash, these products do work wonders, but I recommend trying the choker first. Let us know how things are going!