Actually, their defensive lineman are better suited to play in Kiffin's scheme than what they're currently running, since they have several tackles, but not a single true nose guard. They'd just have to get a defensive end to play opposite DeMarcus Ware. They might even have one in Tyrone Crawford. I suspected there were plans to switch to a 4-3 when they drafted him.
Lee and Carter are perfect linebackers for Kiffin's scheme.
They need to go get some safeties, but that would be true regardless of the scheme.
Kiffin is 72 according to his Wiki page. There's no doubt he's one of the all-time great defensive coordinators, but he is getting up there in years. Could be a concern.