Yikes! I have read some really bad things about that brand.

Take them back. Order Bilsteins on the web, like on Fastlane or one of the many many online sources. You can get overnight delivery if necessary. I would think you want nothing but Factory or Bilsteins on a 400E. With all that power you want good shocks and you really want the correct shocks and struts front to back. You could really screw up the handling by mixing up the front to back shocks.

There was a post a couple of weeks ago from a guy who wrecked his 400E at 15 MPH.

Steve