BigDog, I can't really give you a good description as Brutus is still a puppy. Although, a really big, big puppy. I don't remember every detail about his mother and only saw pictures of his father, as he was in Brazil. One thing I can tell you...look at the walk. Filas, are the only dog with a camel walk. Two legs move together on one side, in harmony. This gives them a roll to their walk. Their hind-end is somewhat higher than their shoulders. But, Bruties hind-end has been really high for a few months. Finally getting more in proportion though.
Saggy skin under the neck(dewlap), and runs all the way under the tummy. Most Filas will have somewhat of a crook in the tail. Those are the easiest things for me to remember to differentiate the Filas from the other mastiff breeds. They also don't have much stop on their forehead/face.
I really need to change the pictures of Brutus in my sig. He looks nothing like that. I think he was maybe 3 mos., maybe 4 mos. old. It seems to be hard to catch all of the details with the dark brindle Filas, unless you are good at photograpy. And, as we all know, I suck at photography. Not my forte.