That sucks. Kinda hard to tell which came first the egg or the chicken. Probably detonation caused it to kick a rod and saw the block in half. I have yet to blow a head gasket at over 1400 hp at 20psi. So I realize you guys are cautious and thats fine but the fact remains that some motor live just fine at twice the level you say you have major problems. Filling the block exacerbates the detonation problem.