for best results you need to keep the wo no larger than 36x36 inches, this keeps the geomitry of the horn the way steve designed it. after that just increase the height of the walls (14") and angle the baffle to allow your subs to fit.
people have had mixed results scaleing the wo, but if you make it 36 x 36 x 14 im reasonably certain you will be very happy

fairdinkum?