If you don't have ASR on your 400E, contact Carl of Bergwerks (
http://www.bergwerks.com) and have him drop in a 2.82 differential. You'll have 80% of the 500E's speed performance (lots more to do for chassis/suspension).
Also, did you add the side marker light?
:-) neil
1988 360TE AMG
1993 500E