The Sideshow should fit since it's apparently an L88, just like the Blu. They're just different brands of the same thing from the looks of it.
But, the 306 is a different atomizer completely, although the same style (exposed).
The 306 connection is the same as the 510 connection. So, if a 306 atomizer fits a Blu or Sideshow battery, then so should a 510.