I spoke with a tech regarding brake size on lr4 vs lr3. Another option, not discussing cost, is to go with smaller rotors. Currently Brembo makes a better than oem rotor for the lr3.
The tech said it would be necessary to swap out all the lr4 brake parts but I do wonder if you might as well then not use lr3 calipers but also go with some sort of Brembo caliper.
Either way, this is another solution to the 18" wheel issue. This would then allow someone who already had a previous set of oem 18's and tires to reuse them.
Some $ could be recouped by selling off the lr4 parts or just storing them for refit upon future sale of lr4 - which would then instantly have new brakes to improve resale value.