I wouldn't breed at all. There are too many in shelters to begin with and since they aren't being registered (it would be with the UKC not the AKC because they are not recognized) it is a little suspicious to me. Please do not forget that this breed is very close to my heart and I own two myself. Now that is my little soapbox.
Second, when I visited very "big name" pitbull breeders 6 years ago, with my friend, the breeders were trying to breed completely unrelated lines. Pitbulls have very few health concerns and breeding them too closely could start to cause them, never mind temperment concerns. The closest I would ever even consider breeding may be cousins and that would be for any breed not just pits.