1961 Chevrolet Truck overheating

Have a 1939 chevy pick up with a 350 motor, ac, on a s-10 chassis. I'm have an overheating iss ue, there is no anti freeze lose, no water in the oil and no white smoke from the tail pipe. I'm thinking there inst enough capacity in the aluminum rad or not getting enough air due to the cond in front of the rad. My question is if I replace the rad what type would offer the most effective treatment. 2 core, 4 core, single core?And how is it sized?