Leaded fuel was available until the early 80's. Lead free engines with catalytic converters began in 1975. About when the octane dropped, because lead was an additive to deal with the octane issue of pre-detonation for over 60 years. In 1983 regular was 94+,premium was 98. After Unleaded fuel was introduced, everything dropped. This is obviously an unpopular concept, but old guys know how it was. The point is don't worry about it. Mopar engines were tough, and run on unleaded better than anything out there. I also drive an original 340 69' original X head, seven years running, no hardened seats, just going down the road.
