After doing extensive digging for years for both my 93 400E and 92 500E's I was never able to find a ready-made supercharger (or turbo) "kit" for the W124 V8's. There is something of a clearance issue underhood. It might be do-able to build one by losing the airpump in favor of a Vortech style blower but getting around the electronics would be hell and a half. (custom chip or not) For what the cost would be to do a kit like that you are better off financially to trade for a 500E. If you already have a 500E then is when you start looking for blower kits, engine work, etc in the aftermarket as you are already at the top of the food chain. If you want more power out of your E420 use the search function to find references to changing the gear ratio on that car. The stock 2.24 is way too tall for most US use. I believe there is an alternative that is somewhere in the 3.xx's that should give just wicked power (by the butt dyno) in comparison. I believe the post you are looking for was by MB DOC talking about an E420 ratio. Use the search function in the top right of your screen.

Happy Reading...Lee