Yep it'll fit. It's just the pattern difference. The rear package tray and under seat pans never changed for e bodies. I have a 70 challenger seat frame in my Cuda. The covers are different, frame is the same.
That seems a bit high for a back seat. I bought a great 70 challenger seat in white at mopar nats for $100 or so, no rips or cuts. Where are you located? I have an extra back seat.