I have an old Heinzmann electric hub already laced to a 20" rim. The Sweet Curry uses a 20" rear, but it has disk brakes. My hub is not a disk brake model.

It looks to me from photos that Yuba may have placed a mount for a v-brake boss on the underside of the chainstays. I think it is actually intended for some footboards, but they may have been clever and put it where a brake boss would go. Does anyone know if this is the case?

Also, does anyone know the rear dropout spacing?

Does anyone remember any brand of cargo bike along the way that had a 20" wheel in the rear and rim brakes? Or even a 26", I can relace the wheel if necessary.