I was advised from the SF SPCA to hand feed my dog her kibble, one by one. I was not to let her have the kibble if she pushed me, only if she took it nicely from my fingers. She was pushy and kind of a bully as a pup, even got expelled from doggy day care. That's when I seeked advice. It really helped, although it took a long time to feed her. I forget the rationale behind it, something about teaching the dog that food comes from you and they should wait nicely in order to get fed. To this day, my sweet OP, has the softest tongue when I give her treats.

Also try putting a leash on him before you give him a kong. This way if he gets aggressive when you take the kong away, you have the leash to hold him back. Practice taking it away. Take it for a few seconds and then give it back if he is good. I have a new terrier mix puppy and he got a little aggressive on me. Fortunately he was only 6 weeks or so and I gave him a big NO and it worked. I also give a chew treat and then take it away for a second or so and then give it back. I do it to let him know that when I take something away it is not forever, especially if he is nice about it.