Typically there is a hose to a plastic nozzle on top of or beside the radiator to collect cold air. I've not seen an unmodified example of your model either, so cannot help exactly, but it's possible the actual nozzle is still there!

Some models (W124 diesel for instance) collect the air from the fender, though, so the ductwork may be there as well.

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!