Leaded / unleaded?

[jps]

Another novice question! I'm looking at donor Sierras (determined on this!) and obviously a lot of them date from the days of 4-star, when I was but a nipper. What are the implications for the fact that it's no longer available? Do people running these cars still use 'additives' / do they run them with unleaded but accept the performance deterioation / or did everyone get their cars converted to run on unleaded back in the late 80s or whenever it was that 4-star disappeared off our forecourts...?