This is the extra large idler pulley I run.... its bigger than the stock XXXs pulley by quite a lot. if running two pulleys on the new squared bar, can use this with a small pulley, but not two large pulleys. So use the large pulley for lift rather than tension.
This is the whole kit for the XXXS for low drag drive system that it comes from: The black belt skips like mad, so it isn't worth getting, just need the pulley, but you'll need the XXX4 yellow belt like Chazz mentions.
http://www.teamlosi.com/Products/Def...rodID=LOSA3280
This is the pulley alone:
http://www.teamlosi.com/Products/Def...rodID=LOSA3282
Chris