The problem with prebuilts is that companies who make them will use proprietary parts.
The other problem is the fan size...there aren't too many 80mm fans that can move any air, w/o a lot of noise. I seriously doubt you will even need another fan.
When you get you parts and get them installed and working...then do this...
Get SPECCY here: http://www.piriform.com/speccy/download ...get the
FREE version from the:
Piriform Link ...Speccy is a really nice system hardware/temperature, information Utility....simply install it...and run the program...then post a screen shot of the main page of the program, when posting a problem/question on these forums.
/e In fact, it might be a good idea to just do it now, so you'll have a Speccy screenshot to compare to, after the upgrade.