Maybe to add a bit extra information: Leaded fuel was only available short time before WW2 , mostly for aviation, less so for private customers. That is why owners of cast iron head vehicles will find a lot of wear on non-existant valve seats with unleaded from prewar times. Grinding in valves was a weekend joy the riders were used to.
Leaded fuel is not necessarily great for everybody´s engine as owners of prewar Tiger Moths with their Gipsy engines can tell. These engines had bronce heads , no seat inserts in them. So when leaded avgas was introduced widely in aviation in wartimes and later, these bronce heads had big troubles from seat wear due to lead content. The effect can be explained with soldering irons and copper tips: You will have noticed eroded copper tips from long use with tin solder containing lead. It eats away the copper , same with bronce valve seats. Now big trouble was with Tiger Moths after WW 2 , you only got avgas leaded that was bad for them . De Havilland specified for these engines unleaded but was not available untill recently from 1980 and later. Bad effect was now the different formula of unleaded that attacked rubber hoses or painted cork floats - so next bunch of problems.
Thanks for the Porsche photo, the engine is mainly Beetle type with alu heads and seat rings . I do not think you´d get wear on them from having unleaded fuel as the kind of alloyed cast iron seats should be fine with unleaded - same with all post war BMW bikes or other alu head engines. Engine speeds in the old Porsche are modest I guess, well below 5000rpm and valves not big, so unleaded quite allright I say.
Vic