those spacers you posted will not work I dont think, the parts from Ford are better, cheap, and metal.
I am guessing your camber is already close to maxed out with your lift kit, so dont be surprised if they cannot align the truck witht eh F-150 spring seats under the coil. If it cannot be aligned you will have + camber which will cause it to drive like crap and wear out tires fiaster then you can buy them. To fix this you will need taller axle pivot drop brackets..this is speculation, but based n a few years of experience with aftermarket lifts, just not your Rough Country one.......