RE: Got I/H/E what next?
 

Get a high performance head and cam that are built to match each other. Your choke point now is your head, not intake manifold and/ throttle body. All the pulley and all that crap won't do anything unless you've done EVERYTHING else. Light weight wheels and tires are good though.

RE: Got I/H/E what next?
 

^ Not everybody is skilled enough, or have access to people who are skilled enough to port heads. General rule for poor mechanics is to put on the best head they can fit in stock form. For a D-series that would be a Z6, but the Y8 is not bad.