My Brother's 380sl has two 4x6 speakers mounted on the rear panels, right behind the drivers seat and passerger seat, like right by the seat belts.
The pretty much face forward.
You can do some very creative things with speakers.
Definately replacing the fronts is a good start.
You can do some more serious massacre on the interior if you like, like door panels etc, but minimal is best if you ask me.
I like ot have stock locations used, stealth install is best in my book, I hate seeing things that just look out of place. Only exception are tweeters, and those would be mounted to look as if they were factory
Alon