The information that follows pertains to reinstalling a Blaupunkt Monterey SQR23 back into a 1984 Porsche 911. Other Porsche models should be similar if not exact and the information could also be helpful when replacing a stock unit.
My car had a Sony CDX-F7705X that the P.O. lost the faceplate to. Love the sound of the flat six and audio components change like fashion so putting the original back in was my chosen direction.