I really can't figure it out but I can tell you I ordered rotors online and got the 4.6 ones by mistake so a already have the rotors, however I have uneven pad wear and feel that the original calipers are due for service and was thinking I could keep the 4.6 rotors and swap out my 3.0 calipers for the bigger 4.6 calipers and get a nice upgrade. I was hoping it is a perfect fit bolt on upgrade that I can do myself. I also wonder if i should go with the double piston 4.6 caliper or I think there is also a single piston one as well.. I really need good advise. Thanks!