My cousins had three Labradors. One was a coward, one a follower and one the leader. They killed a shitload of dogs. All I can tell you is avoid other dogs, show him love, and if it looks like he might have a confrontation, GTFO. These dogs are very nice pets, but their primal instincts are very hardwired into their skulls. It's nearly impossible to get rid of all the angst it feel towards others. You might want to go to a dog psychologist, those exist. My grandma's yorkie was given to one before she died, and now no longer has any of the jealousy and bad habits it had. They can REALLY help. Especially if they have a lot of dogs, it forces them to interact and be part of the group.
Edit: To further elaborate, the Yorkie used to bite at the vet and like you described looked for confrontations with other dogs and such, which my bulldog never has done.