Outside

The head of a cat, for him to notice the things humans can’t see.
The eyes of an eagle, to see the things far from coming, since eagles have the best sight in the animal kingdom.

A large trunk for a nose, because since he has no mouth he needs a trunk for drinking milkshakes.
Gills on the neck, so he can breathe underwater and on land to be wherever he wants.

The log would be entirely the one of a human.
Inside the chest the heart would be replaced by the one of a human for him to love as the dog loves his owner.
The legs of Usain Bolt, long and strong to run as fast as bolt.
Instead of feet he has shaquille O'Neal's hands for him to use them for better climbing or multitasking.