Blown head gasket, likely cause????

Build spec out to?
You mean the compression ratio?
I think the cam is around 284 adv.
Icon forged slugs, (The lower comp ones)
I rang the old boy this morning. I tried him last night when I last posted, but he must have gone to bed already. He's going to check the crowns for damage after his breakfast. (It's only 1050am here as I type this)
He confessed his biggest problem is that after 50+ years of engineering, he's pretty deaf. And he can't hear detonation anymore. Told me that when he started the part time job he works now they did a hearing test as part of his pre employment medical. And he said he could only make out the first two beeps.
Might be time to invest in one of those knock blocks with warning lights?