I'm actually trying to build a 9000-1000orpm redline engine for my NSX.
It appears, that #1 you need to improve the airflow at high RPm's.
It appears as though you need Ported and Polished Heads, Bigger Valves, higher lift cams, and stiffer valve springs to eliminate valve float at high Rpm's. Lighter Forged Pistons probably wouldnt hurt, nor would stronger billet steel Connecting rods.
And to top it all off, bigger fuel injector's and an advanced controller is needed to help your car generate horsepower well into the 9000rpm range.
Anyone else have any input?
I think maomaonsx is also looking into doing some heavy NA tuning..so he might be the one to ask.