They didn't need me after all! He is starting to come around with how the rescue works, "Go here, go there, hang out in here", and we all agreed that I shouldn't see him and disrupt their progress just so I could look at him. Which is a bummer because he is quite the looker. Anyway, he has a potential adopter coming in in the next couple of days, someone who knows the breed.
Careful, AK, I sense you could become a Mastiff hoarder with very little encouragement. We don't want to have to do an intervention when you become the dog equivalent of the crazy cat lady.