I don't have an answer on this, but my big question is "why?" What's the point of a retrofit? The OEM braking system is pretty much optimized for the weight and size of the MO, and most likely the tires are the limiting factor in stopping distances, not the brakes. Is brake fade a big issue for you in your driving pattern? Is it mainly for appearance? If fade is the issue, you might want to try some upgraded pads and rotors and fluid first.
A couple of things to think about, even if you could accomplish the retro, are:
- brake bias: changing to the FX50 kit could alter the factory brake bias and actually lengthen your stopping distances. It's something a lot of people don't think about when putting on BBK's.
- unsprung weight: the FX50 calipers and rotors may add a lot of unsprung weight to the car, which can alter handling and wear and tear on tires, bearings, etc.
Hope this helps.
2011 SL AWD, Graphite Blue, Beige interior