I got mine new... one was around $18 and the other was around $22 brand new from Ford. (Don't ask me why they are different prices, I have no clue, lol).
At any rate, you just remove the shock, remove the wheel (jack it up and use jackstands), then unscrew the nut retaining the coil to the top of the axle beam. Put the spacer that's marked for the left side on the right side of yours (for some reason they seem to fit better that way on RBVs) and the same for the other side. Set the coil back in place and tighten the nut back down. Then reassemble.
It doesn't really change the ride all that much. At least I don't think so. Of course, I never did it in stock form. I went from stock, to 2" lift coils (skyjacker), to 3" lift coils (James Duff), then used the F-150 spring perches to get to 5". If I ever get around to getting them, I have a set of 5.5" James Duff coils being held by a friend for me.
