...you say blow up...we say pop a head gasket.

to make a stock motor push 600+ ACTUAL horsepower is something in itself. so im not suprised at all they popped.

proper tuning/setup, and sensibility go a long way with boosting an LS1. will it continuously make 600rwhp, no probably not, not stock...will it do 500rwhp for quite a long time reliably, yes. with proper, detonation free, tuning. putting in timing till it knocks then backing it off a 1/2 degree, or running a 13:1 A/F, or trying to push a little turbo and lots of hot hair will all contribute to a relatively quick failure.