They all play their part. Without getting to crazy detailed it would be best to just update it all. Some things have changed on some versions and not others. So you can use what you have or print the new ones. The middle and z axis are not interchangeable if you try it it has to be both. But on some you also have to change the corners out as well. The new rollers greatly increase the motor mounts so I’m not sure what part I would actually change first.
This is three people in the same day asking about old parts, when I have had no questions before. Where did you buy these from?