3A/3B is the setting you want.
I use that set up quite a bit and when I do... I like to spend a somewhat more on the 3A guy... and then just have the 3B guy be a stiff who just pitches every 6th start. That way, when the playoffs roll around (assuming I make it), I can set up a 1-2-3 pitching rotation, and move the former 3B guy into my bullpen (Long B or something).
It's worked okay.