Is there a breed of pit bull terrier named blockhead pit?

No there is not a breed of dog named blockhead pit bull.

There is only one breed being pit bull, And that is the American Pitbull Terrier.

Would not surprise me if there is a bloodline somewhere that goes by the name blockhead, But most of these lines truly are not APBT. They are crosses of several different breeds to resemble the APBT.

But when asking about bloodlines which is what your trying to ask, Remember it is bloodline and not breed. Breed is the type of dog and bloodline is a strain of dogs within the breed.