I test fit my 15's on my 14 bolt with discs and just a few casting marks on the calipers needed to be knocked down. I hit it with a flap disc and then they fit primo. Also, are you 100% sure that your 12 bolt and 14 bolt are gonna have the exact same spring perches? The 14 bolt is a monsterously huge and heavy axle, I don't know what kind of lift your gonna be running but the pumpkin on the 14 is massive compared to the 12. Just some things to think about.
