The problem with BC/CC is you can't "fog" the paint to get the 100% correct appearance on the bottom side of the car. Same problem in the trunk. If try fogging the clear coat your going to get "white dust" under the package tray and tops of the wheel tubs. If I was restoring a car that was a solid color (non-metallic) I would definitely spray it with a catalyzed single stage.
I get a big chuckle every time I see pics of a "restored" car with the entire belly side painted just like the exterior. Then they add inspection marks and paint dabs... WHY... it's already painted entirely incorrect!!