I too at some point want to do an NA build, I was talking to the guy in America who now has the engine out of the red zed that made 420bhp. He has the engine now but without the ITB's but he is still making alot of power with a custom inlet. He has put on a 3" throttle body and increased the inlet size on the standard plenum.
If I do end up doing it, I will be looking to do ITB's, manifolds, cams, bigger valves and inlet changes. I would also forge the bottom end with high compression pistons.