Dodge Demon Rear Seat Compatibility?

Can anyone confirm the following for me, as I have tried several seats and they don't seem to work or else, I'm just an idiot and missing something..

Car -- 71 Dodge Demon
Issue -- Rear seat compatibility

Question: Will a rear bench seat from the following cars ALL fit and install in a 71 Dodge Demon? 70-72 Dart -- 70-72 Duster -- 73 Dart Sport -- 73 Dart

I currently have a 73 Dart high back bucket bench front seat in my demon and I am wanting to put a new back seat in as well. Preferably something that matches pattern but ideally something that will install properly. I have access to the mint matching 73 Dart rear seat, but when I tried installing it it just would seem to go in...

Can anyone confirm which seats will actually fit??