radio replacement on '82 SD

I know there has been a lot of input on this subject but I can't find what I'm looking for. At a minimum, what is involved in replacing the radio head
in this car. Most new radio's have four out speakers, the Becker two. Do the speakers have to be re-wired? Also, I recall reading something about having to change out or bypass the front-rear fader. Is that necessary?

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