You can run your slant on port wine! low compression is tolerant of most any garbage gas. lead only protects the valves in extreme conditions like idling for days or pulling a trailer up the alps. Your car should do fine "sans plomb" and don't waste your Euros on hi octane gas, the lowest will work as good.
Very true. Never cleaned the gas tank in my Dad's 64 Valiant and it still ran like a top even with a dirty filter and bad gas. It never stopped.....until it jumped timing haha.