I had a hard look at the first picture and my feeling about the eyes said, Golden Retriever, but the rest...wow, too hard to tell. The pic with him lying down on his side...that looked Mastiff. At any rate...that's a big boy, and time will tell if you don't do the DNA, but...don't rule out Boerbel, the South African Mastiff. I don't see pit there at all, but, as you know, pit mixes come in all shapes and sizes. How tall is he at the shoulder? Could you get a straight on pic of the face where the width of the jaw is more obvious? 60lbs at approx 9 months...? Here are a couple of resources.
"At around
four months of age -- and it can vary from breed to breed and even from dog to dog -- the 28 puppy teeth are replaced with 42 adult canine teeth, which include the molars. You will see six incisors on the top and bottom (these are the smaller front teeth located between the large fang-like canines).Apr 26, 2015"
When do puppies lose their teeth? - American Kennel Club
www.akc.org/content/dog-care/articles/dogs-permanent-teeth/
https://www.thespruce.com/puppy-teething-2804965