I had a 63 K10 with a 283 running air conditioning in the Phoenix, AZ heat with no cooling problems. I put in a 4 core radiator...aluminum rads were very expensive then. I tried a flex fan but at highway speeds and stock gearing the flex fan actually created a problem by flattening out and restricting airflow. I swapped back to the stock fan and added two electric fans which were controlled by a thermostatic switch from a mid 80's Chrysler. This set up worked great even on the hottest days (118 deg plus).
