Here are links to my write up about the install incase anyone needs this info in the future. Keywords: 2002 Mercedes-Benz E320 E class wagon aftermarket headunit install replacing Becker keeping Bose amp and speakers. Hey, the SLK320 empeg install posted here years ago is what really got me started, so maybe this will help someone.

They are both the same:
install at Benzworld
mbworld.org