Steve:

All MB cars have had a fully independent rear suspension since 1953. The ratio is probably 3.73 or 4.0.

A Ford 302 will squeeze in there, and you can actually shoehorn an M117 Benz V8 in, but I believe that requires extensive body work. Chevy engines are much harder, because they have a rear sump, same location as the fron suspension crossmember. I don't recommend a custom suspension, it's too likely to drive horribly.

You can also squeeze a Ford in line six in there if you modify the steering.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!