Can't help on the spring info, but I will tell you that after buying my slider kit from Trailgear, I'd buy form them again. Shipping was fast, and the product was better than I expected. 2 thumbs up. I'd buy from them again, especially if they actually made something specifically for the X. Hope someone chimes in so we can see if these fit.
Well with the long ass shackles that you plan on using... I dont believe that the length will be that big of a deal the shackle will just be pushed out a little furthur than normal (I am just making an assumption)
With the center pin moved.... I donno. with our shock set up on the X (one in the rear of the axle, and one in the front) the shocks would be definitely at different angles. I dont believe that would be good.
The dimensions aren't too bad and those look like good springs for the money. The biggest issues is that we have 60mm wide springs, most jeep and other domestics run 2.5" or 3" wide springs, so a new front mount is in order. a custom rear shackle could easiy be made though.