Don't worry about bulking up until your puppy is at least a year and a half old. They need to grow first. At 8 wks your puppy should still be on formula, but regular puppy food is ok.
What? Are you preparing him for future dog fighting? I sincerely hope not because it is evil! Just feed him normal dog food with higher vitamin content, your Vet can give you tips on the best one, and the dog will be fine.