Do youself a favor and buy a set of Speed Daddy Headers off ebay. $200 to your front door. You need flow mods man, its a must.
Stainless SS Racing Manifold Header Exhaust Grand Prix GTP Regal Impala 3 8L V6 | eBay
Just a simple u-bend delete isnt enough.
For plugs, you could go with AL605's.
And to scan for KR, you need to buy yourself an Aeroforce scan gauge.
You can buy them here, or wait until a used on pops up on this forum for cheaper:
Aeroforce - Aeroforce Intercepter Scan Gauge #
1: Get yourself the aeroforce, its a must.
2: Buy SD headers off ebay
3: Buy pulley and plugs, install TOGETHER. Then get yourself a tune at the same time. Street tunes are the best.