wow, you guys who are saying Mack is a fit at ILB have no clue what you're talking about. He's not too small to play OLB, Mingo is 10 pounds lighter than he is.
Mack is a pass rusher, no matter where he goes 3-4/4-3/hybrid, doesn't matter, his primary job will be to blitz and get after the QB. However, he does have enough coverage ability to cover flats or shorter routes. But he's not a fluid enough athlete to be running with TEs 30 yards downfield. His absolute ideal position would be as a 3-4 OLB. However, like Von Miller, he has enough coverage ability to play OLB in a 4-3. He's versatile enough to play DE in a 4-3 on passing down, probably could even play inside linebacker at times, or maybe even DT on obvious passing downs like Tuck or Everson Griffen in Minnesota. But he's not suited to play those positions regularily