I have a factory size aftermarket replacement 4-core, and I installed these fans:
http://www.jegs.com/i/Derale/259/169...oductId=961386
You also need a thermostat kit to turn them on and off. I used dual t-stats so I could stage them.
http://www.jegs.com/i/JEGS-Performan...52125/10002/-1
Had to slightly modify the fan shroud, but all it took was a jigsaw.