The 12.5" is standard for the 440's on the original Rocket.
The stock shocks are dangerous. If you ride hard through curves and encounter uneven road or bumps, the back end will skip sideways on you. I got the Heavy Duty 440's (after trying the standard ones) and they're great. My g/f and I are around 360 lbs. together (I'm 220) and ride two up half the time.