Interesting thread, I would be curious of this too. I have done this "up-conversion" on almost every vehicle I've owned (including my 3 and 5 series BMWs) and it's always just been the bumper. Until you mentioned that I didn't even realize how the fender / bumpers come together on these X's, that's kind of a bummer that you have to do all that for a bumper swap. Changes my mind completely on doing the mod.