need help with an "adapter-piece"

 From:  Frenchy Pilou (PILOU)
5029.2 
maybe a method
Join the 4 edges of the Top cube
Draw a curve or a Line as Profil needing from the Base cylinder to a middle of an edge's square
then
Sweep 2 rails or NetWork or Loft ;)

EDITED: 25 Mar 2012 by PILOU