I have had a bunch of euro 280's and they all ran like scalded dogs (Larry Bible expression). None had the slightest problem running on 91 octane gas at the timing spec. I think you have your octane measures mixed up.

You may have a lean mixture, carbon build-up, cooling probems, or other issues causing spark knock.

But to answer your question. A catalytic converter was always added. Some cars got oxygen sensors connected to an aftermarket lambda computer and frequency valve. Some got cannisters for fuel and crankcase emissions.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe