You'll be running 6 cells in series with that motor,2 3s packs in series.You could run 2 3s1p packs in series(22.2 volts),good high capacity packs with a high C rating,or you could run 2 3s2p packs in series(also 22.2 volts) ,twice the capacity and amp handling (but twice the size and weight too)
2 6s1p in parralel would be the same as 2 3s2p in series.confused? Check out Batfish's sticky
http://www.rc-monster.com/forum/showthread.php?t=2250
Edit:aluminium diff cups would be a good idea.