Originally Posted by Greed

Hello,
I'm a long-time lurker first-time poster. I have had the Nismo front bumper successfully and neatly installed onto my base / sport 370. All you really need to buy is the bumper (about $350 or less), front bumper diffuser ($470 - $624) and (optionally) the front fender liners (about $130 each. You'll need two sets -- one for each wheel well).
The liners can be hard to get. I was told by my dealership's parts person that the liners currently aren't stocked anywhere in the U.S. so you have to order them direct from Japan, which can mean unpredictably lengthy delivery times. However, a body shop can fabricate reasonable facsimiles easily enough.
The liners, labeled "protectors" by Nissan, cover the gap in the outer wheel wells created by the wider Nismo bumper. They also allow the bumper's fenders to be riveted into place just inside the outer wheel well. Trust me, these liners (or their fabricated replacements) are a MUST. Your car will look like crap without them.
I can say with absolute certainty that your stock engine undertray will work just fine. It can be pulled forward slightly and completely fastened to the front diffuser that attaches to the bottom of the Nismo bumper. No need to spend $1133.98 on the Nismo's flared undertray.
You don't need to get much extra hardware to bolt the bumper on. All your existing bolts and fasteners can be retrofitted, and the extra you'll need are readily available at the dealerships and can be easily obtained by a body shop, if they don't keep them handy already.
Hope this helps.