I think there are two cats running in parallel up front with a mid and rear muffler. Unfortunately, neither this Russian EPC (link below) nor the MB EPC refers to a catalytic converter. Best of luck.

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=124034&M=119%2E975&GA=722%2E354&CT=F&cat=44S&SID=49&SGR=015&SGN=01

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles