If you've already ordered the part and paid then probably best to ask them to make sure it's the right part. I know for the standard 3RB bumper, this one will definately fit.
http://www.japanparts.com/images/ImageF ... 1&no=11092In future, best to contact PHAT-GT in the Vendors section. He is very knowledgeable, and get you parts faster, cheaper.
As far as instructions are concerned, it may come with the item, but if it doesn't it's very easy.
Take the screws out from the standard grill by carefully using a flathead screwdriver to pop it out
Once you've taken the standard grill off, i believe the corazon grill should come with some double sided tape you can place under the flat part of the grill. If it doesn't , just place some under there for more stability.
After you've done that, just position it and pop the screws back in