By the looks of those pictures definitely a head bolt torque issue. There is something to adding an extra 10 foot pounds to the longer center bolts
I was told by Brian Weaver almost 20yrs ago to add like 20 lbs to the GN heads....felt scary doing it but with that and doing it over 3 days it held 28lbs with a graphite gasket 20k miles till i parted it out...i wouldn't hesitate to throw an extra 10 on them for sure
Oof! A month or two ago I cracked cylinder #3 in my Pontiac OHC turbo engine. Luckily it was still my cheap long block. I keep thinking when I eventually change to a more appropriately sized turbo on the L6, I'll put the spare turbo on my Centurion and be happy with 5-12 psi or where ever it lands on the 8.5:1 completely stock engine. I hear you on the cost of going up. I'm thinking of going to a bigger roller cam in the Skylark and wondering if I'm really up for the additional valve spring maintenance and potential to lunch the bottom end. The cylinder walls looked like that the day I put it together 9 years ago, except the crack was just a linear'ish stain
