Ok. This is all some good info.
A lot to digest. Now that I have a visual of what a valve seat failure looks like, my 68 slant head is definitely a good head. So I think I'll just mill it and use it.
Milling a head these days is a couple hundred bucks so I just wanted to be sure.
I do plan to daily drive the car but if it's made it this far, 56 years later, surely it will take more than me to kill it.