They won't work, the seats are the same size, but the actual framework is different. It would take a bit of modification to the 72 seats to work with a 70 cover.

I had 70 Barracuda seats and 71 Challenger seats, the 70 Barracuda seats were in better shape, but the actual way the foam and such is mounted is completely different then the late 71 Challenger seats foam. So I had to reuse the late 71 seats.

Ryan