My set up with the 540" HEMI is STOCK. The 26" radiator is even the correct part# for a 66'. Viscous fan, stock shroud and 180 degree thermostat. I also have the rubber "air dams" that the factory installed on the front and back of the hood. Driving in high 90's produces temps of 190-200 on the freeway at speed. As soon as I am on a back road, 45-55 mph, the temp comes down to 180-190. The factory knew what they were doing!