74 power wagon dream truck...

I've lost 8553s in the same manner at less pressure, without detonation, using alloy heads.
The Static Compression Ratio is nearly useless in regards to avoiding detonation.
It's all in the measured cranking cylinder pressure, and the expansion ratio and time.
I cannot see running over 200psi at WOT, with a 4bbl carb, and with iron heads and pumpgas. Not with any gasket. Not with any decent timing. This is my opinion.
Your engine will produce peak torque somewhere between 3000 and 4000 rpm. Wherever it peaks, is the same rpm where your engine will be most efficient and thus producing the maximum amount of RUNNING WOT cylinder pressure, which is typically 5 or more times it's CCP. Five times 210 is 1050psi. I don't think the 8553 gaskets can handle that, no matter how well the decks are prepared. Not to mention detonation.

To get 200psi in a 360 with a typical Ica of say 60 degrees will require a static compression ratio of 11.5@200ft elevation..... so I'd be looking for a new compression tester, lol.
With a true Scr of 9.2 and the same 60*Ica, and 200ft, the pressure should be closer to 152psi.....and 5 x 152=760 which is well within the 8553's capability, so long as detonation doesn't drive the pressure much higher.
The sound of detonation, is caused by the sudden rise in cylinder pressure, of colliding flame-fronts inside the combustion chamber, hammering the piston/rod assembly back down onto the crank, and slamming the piston skirts into the cylinder walls.Plus the chamber rings like a bell.
I don't believe your failure is detonation, because of where it failed, the same place mine did, into the valley. When mine did that, I checked the rod-bearing in that location and it was fine....... but I have the hi-volume pump and oiling mods, so that might have had an effect. However, after I installed the 1008s, I ran the same timing curve, for another season.

Btw, my engine was running a tic under [email protected](alloy heads). I have since lowered the pressure with a later-closing intake valve and a redesign of the Quench .