if you are adding headers, add the intake too and even a cam down the road to fully reap the rewards.
-Both units must be removed to replace one, and since they share the same gasket, (the NEW header and the STOCK intake) one will blow the gasket -probably the exhaust.
check out
http://cliffordperformance.com/home.htm
adding the header alone will mke the motor a lil more efficient but you probably wont notice anything except the exhaust leak