That fitting is for coolant, you can plug it with this
http://www.improvedracing.com/coolin...663-p-344.html. If you plan to take the car on a road course then you need an oil cooler. I would also recommend that you put a thermostat inline with the oil cooler lines so the oil will warm up quicker such as this one
http://www.improvedracing.com/thermo...85f-p-212.html.