[Ledslinger]

Pondering the purpose of the belly pan, I think it is keep debris from coming into the engine bay mainly when off road. The path it is protecting is between the frame rails and mostly in front of the front tires, so it isn't to deflect debris thrown off the front wheels. I think it is mainly protecting from tall grass, brush, small trees or sticks or possibly if driving over crops.

If you drove over plants taller than the bumper, the bumper would knock them down but they would stand back up behind the radiator. This would put them in the area of the crank pulley and possibly the fan. It make also give some protection to the brake line crossing over on top of the tubular cross member on the K1000. The pan also protects the radiator from plants when in reverse.