Tell me about these heads - 2658920 66-67 273-318ci

Cool!
I've had this engine for probably 20 years, didn't realize there even was a closed chamber head used on 318's until I pulled the heads off. I thought maybe the had been milled. I got the whole engine for $50 from my Uncle.
Here's a pic next to some 80's 163's I also have for comparison. I was told the 163's have hardened seats? How can you tell by looking?