interchangeble parts from coupe and sedan????

[butterm3]

Here's the question,

In my previous M3 sedan I had a custom box made that was ported through the armrest, I now have a coupe and still have the box and instead of spending money on a new box and having to cut through the rear deck I was wondering if the back seat of sedan would fit and if I can put the seatbelts as in a sedan on the body of the coupe,(i know that the fold downs share the same part numbers so I am assuming it is possible) I really need to know ASAP since I was able to find a really cheap rear seat but it is out of state and could not send it back if it did not fit.....

thanks
Juan