They should be interchangeable - everything else in the interior is. I think I told you the other day that '49-52 would fit a '53 or '54 Pontiac? I got to thinking about it later and decided that the only swap I'm certain about is between '49-52 Chevy and Pontiac and between 1953-54 Chevy and Pontiac. Those I'm sure of. I'm not positive about either from '49-52 dropping right into either '53-54 (although I'd bet on it.) Those rear seats are pretty straight and pretty simple.
Coupes are different then sedan. Dont ask me how I found that out! Hardtops and convertibles I believe are the same but they have armrests, so the top part is different, but it would work if you used the armrests too. 4 door rear seats fit, but they have that little hole in the rear corners, but you could put seatbelts there or fill it in with foam before reupholstering it, and it looks good.
Yeah, I forgot to mention that: sedans are the same, but true coupes have a thinner seat back and 4-doors are a bit different, too.
thats true. real coupe seats are different, and it turns out they are pretty rare. The one in my car was down to the springs and all rusty so I tossed it thinking it would be easy to get another one but I was wrong!