hard exhaust seats in heads
 

what year did they start putting hard exhaust seats in heads? I am thinking the switch to unleaded gas was in 1975...is that correct? The reason I ask is I'm putting a 454 together to run E85 on the street only...The heads I have are 1977 castings...was wondering if they have hard seats or not...(don't even know if I need them with E85 or not)...

Any idea on the valve seats?Should they be hard seats in a 1977 head?