I should also mention regarding this wheel swap, it looks like the 14 rear caliper mount should swap over to the 12R, making rotor changes/mods unneeded. The front wheel has 320mm rotors on the 12R, 310 are on the 14. In order to get the caliper spacing right you will need to have bushings made, or use precision washers.
I belive the front brakes will work ok with the smaller rotors, but when I tried it they howled like hell. I might have had the calipers spaced unevenly since I just used some washers I had laying around. Also, some of that anti-squeal paste behind the pads may help.