Michael

European cars, historically ( 1960's 70's & 80's, before electronic ignition ) have always had very small plug gaps.
If you look at plug gaps for BMW, Mercedes, Porsche, Audi, VW, etc., this has always been the case.
For your 1973 model, I would be inclined to either go with the manual specified 0.024" or, you could try a compromise of both, & go in the middle with 0.028".
You will know if your car can't handle the wider gap, as you would experience a " tip-in" misfire on new plugs, in fairly short order.

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2007 C 230 Sport.