you need to use the sfa calipers with sfa rotors in the rear with the front range kit, if I understand correctly. The sfa rotor is thinner than the ifs rotor. So if you use an ifs caliper on a sfa rotor, you will have a gap. As to whether the pistons will pop out, it's possible. The best route would be to use what the kit suggests. Save the extra rotors so you can use them once you warp or wear out the current ones.
