This has been a bit of a pet subject due to the number of old cars which have passed through my hands (manufacturer stand):
1979 Daihatsu Charade (unleaded ready)
1987 Saab 900 (Not unleaded ready)
1983 w123 200 (Not unleaded ready)
1983 w126 280se (Not unleaded ready)
It was interesting to note that Japan was ahead of the game in the late 70's with their cars unleaded-capable!
I fill mine with premium 97 RON.......I agree lead substitute is an overkill.