They fit. As noted, they flip forward. So far so good.
The plastic trim at the bottom is different because of the difference in how the seat belts attach in the convertible. Convertible belts attach to the floor not the seat like the 3d/5d. I've converted the plastics by cutting a factory slot.
I'm sure you could just swap them but make sure the holes for the threaded belt mount are there. I'm 99% sure they are.