Aside from factory screw ups (and there were plenty) the applications were as follows.

1966-1970 B-body Torque Box applications:

All Hemi hard tops: Rear Torque Boxes with Inside Reinforcement Plates & Rear Leaf Spring Plates

All non Hemi convertibles: Front & Rear Torque Boxes, no Rear leaf Spring Plates & no inside torque box reinforcement plates.

All Hemi Convertibles: Front & Rear Torque Boxes, Inside Torque Box Reinforcement Plates & Rear Leaf Spring Plates.

*In addition, most Hemi cars (hard top & convertible) recieved Pinion Snubber Reinforcement Plates, I've seen more on 4 speed cars, but also on automatics as well, seemed to be hit or miss on those.

*I have observed some original examples of non Hemi cars with torque boxes, especially during the 1970 model year. I've seen them on 440+4, 440+6 cars, as well as a few 383 cars. 440+6 was probably intentional but it was still hit or miss, non 6 pack cars such as /6, 318, 383, and 440+4 cars were likey just factory production errors.