Lots of aluminum bits on the 450SL and other much earlier MB engines dating to the 50's. Non-diesel heads were aluminum with various water pump/thermostat housing bits also made of aluminum. The mid 50's to early 60's 300SL had alloy blocks too as did the M189 engined 300SE from 1961-1967. The M130 engines from the late 60's to 70's tended to have numerous head related problems including corrosion but I'm not sure how much of the corrosion problems with those engines was due to poor cooling system maintenance or what. Mark