Aside from a custom jobbie, the XTM Mammoth is 182mm long that you could mod. Not sure if the other dimensions will work (like the ball, pin, etc): http://scriptasylum.com/rc_speed/_dogbones.html
158mm is just a little too short... 162mm could work... 158mm would just allow too much movement on the shaft... Also looking at that drive shaft makes me think whether it would be able to handle the 1520 motor...