there are a few useing the sonix head and tail.
if your going to do the tail, get the 60 dollar one. the 50 dollar one as a metal tail gear, and alot who have used it say`s the belt is to wide for that gear and it slip`s alot.

alot of people includeing me are useing the hxt900`s, they have two different 900`s. ones .12sec and the other that i have is .10sec.
their they same blue in color. the 10sec one are further down on the page, or the next page i cant remember now.
either way you will have to do some sanding and fileing on the mount that house`s the two together to make them fit, put people have done it