Gsr block
gsr head
pr3 pistons
skunk2 stage 2 cams springs retainers or stock itr cams
itr/aebs intAke manifold
stock tb or itr tb
kiddracing header (or whatever you want I'm biased)
stock injectors
tune with Scotty

I would do a stock gsr longblock and not touch the internals at all I've made 180-185whp with those mods on a stock gsr without opening it up. But if you have to build a motor that's what I would do