My 69 383-S that is B5 blue was not painted body color on the bottom. It was a dark primer gray color. I don't think all Mopars were painted body color on the underside.
You are correct. These cars were not painted body color on the underside. They were dipped in a gray or black primer(depending on assembly plant). The only body color that was on the bottom was overspray. The amount of overspray could vary from car to car.
This is how I'm doing my Dart. It will have a single stage paint on the bottom that matches the dark gray color of the dip primer. Then there will be body color overspray on top of that. That was my biggest mistake when I built my Challenger. It's body color on the underside. I wish I would have gone the primer/body color overspray route with it.
