I think it's Perk. His timing on blocks has been vastly improved over the second half of this season and he is developing a semblance of a low post game on offense --I think Doc will attempt to go to Perk to see if he can establish himself early in games. The big loss of KG on offense his the impact he has on spacing and the attention he draws. I think a combo of Perk hitting a few low post iso's and BBD hitting a couple of early 15 footers will help mitigate the loss of KG on offense and open things up for the 'little 3'.
The real 'big' they need is luck and avoiding foul trouble. I am a fan of starting BBD at the 4 (his jumper is the difference for me -- he'll need to be guarded on the key -- middle opens for drives and space created). BUT, the danger is early foul trouble -- they have got to avoid the early fouls.
My hope is that they can put 4 games out of 7 together in each series in which they can fire on all cylinders. KGs consistency/intensity will be missed -- without him, we can't expect this team to be always in a position to win (they'll be less consistent as a team). Shots won't fall in some games -- and when we get to Orlando and Cleveland, we won't have much room for error. The 4 out 7 games that we'll have a chance to win must be taken advantage of and there will need to be some good fortune (luck) on our side if we are to get past Orlando or Cleveland, IMO.