Something is wrong with your measurement, or maybe with that drum to drum measurement.
I was thinking about it, so I looked at the kit. Those rotors sit on the axle flanges, and they're the mounting point for the wheels. There's no way they add more than a 1/4" to the track. The axles stay in the same place, so the only difference is the thickness of the rotor compared to the thickness of the drum at the axle flange.
