The block will bolt into place. The '08 has the MDS system and an external EGR but if you leave the MDS Solenoids in place they won't cause you any issues and they can be pulled out and plugs from the 2500 5.7L can be used. You will need to plug the EGR port on the '08 block with a block off plate that's available. I would stick with your '03 intake manifold, wiring harness, and coil packs/wires unless you want to use the aftermarket adapter harness to utilize the '06+ dual coils.