If we consider KG and Wilcox both PF's, that would make a heck of a front line for not having a Center.
Doc's offenses seem to use movement and spacing to create opportunities, not inside-out post-up stuff, so a duo of PF's could be a pretty great option offensively.
Defensively, you can scheme anything. KG is a touch thin to guard Howard, but sure did a heck of a job. So did Perk, but they guarded him differently (KG denied with length, Perk positioned, bodied and muscled him).
So I don't think we need a stiff to play Center, but we do need length, and mobility and range at the position should be what we get as an advantage.
So we don't need a center, we just need a nice, mobile guy, close to 7' tall if possible, or at least a wingspan at least that wide, who can run the floor and has range to at least 20ft.
Yeah, we don't need a center, we just need to sign the next Dirk for Rondo to pass to.