The "whats in there" answer is easy, nothing you want to keep.
Porsche sends a stereo speaker level signal to a front/rear fader next to the driver seat, and I think the amps are next to the passenger seat, so wiring nightmare back and forth, and none of it useful or high quality.
Pre 84 has the speakers mounted behind a flat perforated grille and the depth is VERY limited if you don't want to cut holes in the metal doors or mount grilles over the door panel. My factory speakers were totally toast the foam surround turned to dust so the "speaker" paper wasn't attached to the speaker frame.
Out it all went on my car.
Rubber ducky 11" antenna replaced the factory goes up and down all the time thing.
JVC KD G720 AM/FM/CD/MP3 with a front USB went in the console and powers the door and rear speakers directly, with a sub output to a 8" powered Bazooka tube in the hatch area.
Two pairs of Alpine 3.5" speakers went in the doors, with I think 5.25" in the rear.
I rate the sound as very good, and thats without any real tuning yet. Putting the bass through the powered Bazooka works wonders, and it does play pretty loud, MUCH louder than what many 500 watt dual 15" types might lead you to believe.