The B66 comes with the double-rail clamp to fit on the regular seatpost it looks like he has. The double-rail saddle's frame is stiffer and the saddle frame flexes on the springs where it is supposed to rather than on the rails.
Riding an upright bike with that narrow saddle would be tortuous. I would imagine ANY wider saddle would be an improvement. The B66/67 is a very comfortable saddle once it is broken in. But even before that happened the increase in comfort from what is on there now would be HUGE.