I was interested in pruchasing that exact airbox for my E500 at one point but I was told it wouldn't fit.

The seller told me that it didn't fit his 400 because of the opening on the underside didn't match up.

He also told me that it is no bigger then the stock 500E/E500 airbox.

I don't think he was lying to me or intentionally tried to lie to me because I was purchasing something else from him, that he was shipping to me anyway. Plus he was pretty knowledgable about things as he is looking to purchase Bergwerks 1st gear start for his car and he is all the way in Germany.