Lol, if the conversion kit had come before the F2s Bens car was going to become an X5 squared.
If you like the modding have a look here
http://www.4wdrc.com/tech.htm
And especially at this
http://www.4wdrc.com/tech_belt_adjuster.htm , Id taken this idea a little further
The difference is the ball end I use on the tensioner is a Losi TI one with a hex head in the top, so by drilling a small hole in the ball cup I can instantly tighten/slacken the ball end and instantley adjust the tension in small increments.
Also after swapping the centre pulley for the xx4 one, the easiest way to massivley reduce belt skip and allow lower belt tension is to mount a roller bearing just in front of the drive pulley so if the belt tried to lift over the teeth, the roller stops it.
There is loads of other stuff in the X Factory section