Why not an edelbrock victor X manifold? Heard there amazing for boost. z6 to me doesnt feel much faster then a b7, thats why I scrapped the idea of doing a z6 or d15b swap. Good thing your boosting it tho, that's all D's are good for.
but there are no aftermarket rods for the d15's. (yet, fjt is coming out with a set)
i'd go with the z6 trans due to the steel shift forks, the y8 has aluminum shift forks that bend easily.
i'd stick to the stock intake manifold, works fine for everyone else plus there is no evidence that a y8 intake manifold flows better than a z6. the best results ive seen is from port and polishing the head, but that was complementing additional head work. if you have money that you want to spend, buy a wideband and/or an EGT gauge.
get vitara pistons and i beam rod combo from fjt, that is the best bang for your buck.