Christian Steffen
I'm Awesome
You won't reach 600 with TBI but you could come close with Vortec heads and MPFI from 96-99 and an aggressive cam. Hey, if your rebuilding, you might as well go all the way. Make sure you use the upgraded Injector Spider from from 2003-2007. Although the 454 may have already had that in 96-99. Not sure. I know the 350 MPFI did not.
96-2000 454s don't use the spider, they use the normal style injectors found in every ls. Vortec heads definitely won't support 600 hp though, not without boost anyway.