I believe the 78 CB400 used spoked wheels, but drum brakes. Any of the 'e' series should also fit, again , drum brakes. You might check out a 360G wheel that has disc and spoke, but I don't know if it's a direct fit. You will need to check axle sizes and spacing for the sprockets and wheel centering.
Hang in there, though. Jim should be along soon. He would know for sure.