I am pretty sure that no one makes a bolt on performance exhaust for your car. What you would have to do is get a good exhaust shop to either make a whole custom exhaust (expensive!) or just put in a straight pipe where the cat and/or resonator is, and then have them put on a performance rear muffler. You could try Remus, they make some for older Benzs. If not, then just get a universal muffler and stick it on there. With the cat issue, taking it off wouldn't hurt anything! Up until 89 I think you could even order a new Benz without cats. I would put one on though because this place is already polluted enough. I'm not a tree hugger, but this isn't much. Get a high flow cat and I bet you could barely tell the difference with that than with no cat. Also do a search on this topic, exhausts have been discussed quite a bit. Good luck.
'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.
"A Mercedes-Benz is like a fine wine, it only gets better with age."