When hardened valve seats production??

Leaded fuel was available until the early 80's. Lead free engines with catalytic converters began in 1975. Coincidently that was 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, the average octane rating decreased. . This is obviously an unpopular concept, but old guys from the 60's know how it was. If we can pass one piece of knowledge on, it is don't believe everything you read, and The point is don't worry about it. Mopar engines were tough, and ran on unleaded better than anything out there, so Save your money for something productive. I also drive an original 69' 340 original with the X head, seven years running, with no hardened seats, just going down the road.