the perch is the part that the spring rests on, the silver part in the pic, on koni yellow this is adjustable so that you can adjust ride height even with springs, but ur gonna pay for it, there about $500 a set, new... now you can get
omni, skunk2, or gc coil sleeves and run them on stock shocks for about half the price but u'll probably blow the shocks quick and have to get new shocks anyway... so if ur gonna do both as soon as you get money i would say get the coils first run them on stock shocks then when you get enough money get some new shocks...