for the intake i would go with a J's racing intake. gives you better throttle response and better low-mid range as well as great high end.

for the exhaust depending on what your setup is for. if its for autox i would go with a setup that has piping no bigger than 2 1/4" need som back pressure. if you're just going for top speed than get a 2.5" system. buddy club is nice but might be too much to handle DB wise on a daily commuter.

for the header the 4-1 sounds good. best ive seen so far is the spoon model. but you might want to check out the bisimoto header if its in production.

for valvetrain i would go Toda. the sell a complete tuning kit for the C5.