You just need to know how much extra down travel you will have over stock.
With the RXT Icon set up a +2 should be more then fine.
But if you going to have more travel then that go +3 or +4
All this means is that they add an extra couple of inches to the 2 lines from the rear axle to the center of the bed.
Please send me a email with the following info
-Full Name
-Shipping Address
-Email for Paypal invoice
-Phone number
-Screen Name
-"Year" of truck
-"Length" of lines 0"-2" (check link for more info)
-"Color" of brake Lines
I have a front kit, not rear. What's your email?