samstar,

Tower Hobbies sells the whole power system as a replacement [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJCJ6&P=Z]here[/link]. They list a 6mm adapter so probably a collet-style adapter like those sold at [link=http://www.hobby-lobby.com/propadap.htm]Hobby Lobby[/link] would work fine.

Carl,

I suppose it might come off water in stock form but you would really want the ESC/Lithium upgrade to reduce weight and increase power. I don't have any experience with the Multiplex Cargo but I have heard that it is powerfu so that it can carry a decent load. There is plenty of room for a 9-cell pack but you'll still need to upgrade the ESC since its limit is 8 cells.

The two 2100mah packs in parallel would also make a nice hop-up with great duration.

Good luck!