I know his mind is made up and he hasn't asked for breed recommendations but I'd choose a Working Strain Belgian Malinois or Dutch Shepherd. If more size and intimidation are required in a hot environment then I'd look for a Working Strain (Scott bloodline) American Bulldog - preferably from hog hunting stock. But that's just me.
I also have no issues with crossbreeds if done knowledgeably. An example: Catahoula + gamebred Pit Bull crossed into a Scott working American Bulldog (hog hunting strain). The result would be a lighter boned "bulldog" with a better nose and harder than the American Bulldog - not to mention more agile and with more endurance. Just an example for a hard, fast hunting/kill dog or farm dog.
If it is a purebred Scott AB it will have some APBT blood from the earlier crosses.
That is why they do not look like a purebred Johnson AB.