Power steering cooler and engine oil cooler sizing

[ShowStoper71z28]

I am in the process of adding a power steering cooler and oil cooler to my 01 Camaro with ls1. I autocross and track this car, but I also drive it on the street. I am fabing a horizontal mount behind the radiator for the oil and power steering cooler. When I am street driving the car I plan on blocking off the oil cooler and power steering cooler. Everything I have read states without a thermostat is hard to keep the temps where they need to be. This is why I am mounting the horizontally behind the radiator so I will be able to block them off. The question I have is what size cooler will I need? I am in the south and in the summer time is very hot. I will be racing in 95 degree weather for 20 min session.

Thanks for your help

chase