If you can get a good deal on the LS2 bare block IE like $400 and it is in good shape go for it. You might be able to make 600 rwhp with a 402 stroker LS2 but its not going to be very streetable at all. However, you could do a 402 stroker LS2 with forged internals and go forced induction from there and 600 rwhp should be easy and streetable. The 6.0 truck engines are a good start and cheaper as well but either way you are gonna at least need forged rods and pistons to make the power you want. The truck intakes do breath surprisingly well but after 5000 rpms they begin to back up and become a restriction. The LS6 intake is a better choice even over the LS2 setup. However the New L92 heads and L76 intakes are making great power as well but the heads have a thin deck that is not ideal for making boost but should be fine with no more boost than you would need to run to make you power goals.