Gillis. I believe he play a lot of 4 for us this year. He played there for Purdue too. He's jacked, plays solid defense, and can shoot/space the floor.
If that's who starts, Sion will be the first perimeter player off the bench. He can come in for any of the 1, 2, or 3. I think we will keep one of Foster or Proctor on the court basically all the time. When Gillis comes in, either he or Flagg can play 3 or the 4. And yes, Brown and Mal can play together with Flagg shifting down to the 3.
I think Kon will be much, much better than Power, but if not, I think Sion could start.
Of all of these, literally Singler was the only one to not play the 4 when we won the national championship. Hell, Battier guarded their 5, Woods (for longer than he should have), in 01 championship game. Amile played center and guarded Kaminisky when Okafor was in foul trouble, while Winslow matched up with their 4 (Nigel Hayes) like he did all year.
You're basically making my point for me. Just because you have some other big guys on the roster, your best team may be having only one of them starting/playing big minutes.