Could try
http://www3.towerhobbies.com/cgi-bin...?&I=LXPR91&P=7
http://www3.towerhobbies.com/cgi-bin...?&I=LXEVB8&P=7
http://www3.towerhobbies.com/cgi-bin...?&I=LXFYU9&P=7
The thick HPI ones could have clearance issues though - I noticed with the ext chassis I think the centre diff has moved very slightly, and theres SFA clearance between the front shaft and the chassis brace.