Potential Dog Size?

I adopted a puppy from the SPCA a few months ago. His dad was a mastiff (170 lbs +) and his mom was a labrador/pitbull (50 lbs., poor girl lol). Anyway, now he is a week shy of 8 months and 70 lbs. (very lean). I know that there is no way to tell for sure w/ a mutt but any guesses on how big he may get? Thanks