All rear disk kits are going to increase the track width slightly, usually only a 1/4" to 5/16". A disk rotor is just thicker than the drums where they sit on the axle flanges, that's the difference and where the increase in offset comes from.
Dr Diff's kit lets you keep the OE style tapered bearings. If that's important you'd better check the other kits, because most require non adjustable green bearings.
