Again: Unleaded or leaded fuel for mid 70's /6?

SlantedMark4 said
I have a 1974 225 slant six under the hood. I've found out that hardened valve seats were inducted in 1972. Does that mean all engines from 1972 and up can be operated with unleaded fuel? And how is it with 95 octane fuel instead of 87 octane? 95 fuel is lowest and standard here in central europe. Do I need any additives or am I fine running 95 octane without any additives?
I know this topic is in discussion all the time but I have never really found a good answer.
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Aso i ha jetz scho mehreri Slant Six ka u bi aui immer mit Bleifrei 95 gfahre u ha meistens garke Zuesatz drito. Die si so nidrig verdichtet, da meuschder ke Sorge mache. Wenn di dennoch sorgsch, chasch ja Bleiersatz dri tue. Aber Bleifrei 98 bruchsch sicher nid.