When I say Vortec, I'm not talking LS. And the 6th gen is a good motor, it didn't have the stupid morphadite head gasket scenario as the GenV nor did it overheat or in general suck like GenV. The heads were less bad and in general the motor was reverse compatible with MarkIV old school heads. But you can't swing a dead cat around these parts without hitting a decent junkyard 350 Vortec. I live in the Springs, they're everywhere and they last forever. Not trying to discourage you from the big block swap by any means as I have one myself, just trying to make you apprised to your cheaper options.