Be sure to watch the Bilstein footnotes. Many of the 6100/7100 coilovers are lightweight shock assemblies recommended for front buggy applications only.
Using the stock front mounting positions, a coilover spring will not clear the frame rail and upper shock mount stamping. I haven't worked with the RCD kit but I believe that it uses an upper submount adapter that pushes the top of the coilover outward to generate the needed clearance.
It would probably be worth a call to RCD to ask them which shocks might be known to be compatible with their kit.