Savage XSS question

OK thank you, i've take a look at the innovative rc kit, it seam to be very well make.
But why they tell that this kit fit the Savage XSS but with the non-X arm
Which arm do i need to fit with this kit, and do i need front and rear arm?? upper and lower?
And is the non-X arm is as good and solid than the X one??

Thank you!
David