No duramax is 100% safe at 600hp. But with a 68mm cheetah(or Danville charger), a set of 40-60% over nozzles to get the pulse width down, and good efi live tuning you should be able to make that kind of power without too much of a risk of blowing it up. Of course you're also going to need a built trans, lift pump, egr delete, and some other little supporting mods as well.
Most people find that they are very happy around the 500-550 mark on stock turbo, injectors and cp3 though. Lift pump, exhaust and efi live tuning will put you over 500 for a lot less $$$$. I would build the trans and try it out at this power level before you go ahead and swap chargers and injectors and realize it wasn't worth the extra $5000