70-74 Challenger rear seats all use the same frame and foam. Any style of upholstery can be used on them. The only exception is the convertible seat. The bottom convertible seat frame is the same as the hardtop. The back of the convertible rear seat is narrower to fit the convertible top frame in the car. The front frames and foam are as follows: The 70 is by itself; the 71 & 72 are the same; the 73-74 are the same. If you stay in the same year group the front seat backs are side specific. You can interchange the bottom frames from side to side. You can also change the bottom front seat frames with any year of bottom seat frames. This makes the front seat backs the only year specific item. I post this in case you would need to mix and match to build a seat set before you reupholster them. The seat foam must match the year and type of upholstery you use. The Cuda seats are separated in the same year categories. The frames will interchange with Challenger. To use the Challenger upholstery the seat foam must be changed to match the type and year of Challenger upholstery. Also, I am 90% sure that the front seat frames in a 71 B body are the same as 71 Challenger/Cuda. If so, a 71 Road Runner/Charger front seat bottom could be used as a replacement bottom seat frame for any year of Challenger/ Cuda. As has been said, any of the seats will physically interchange if you do not worry about the year/style break down.