[tdangle]

For my 70 350 stock timing was 0 and it never overheated. At 60 mph you don’t need the fans as airflow is more than enough. My thoughts are either an undersized rad , blocked cooling system, blocked exhaust. A lower temp thermostat will not let an engine run cooler it only sets the min temp. Sb chevys really run best right around 200 degrees. You could have a carb problem. To rich at 3k can cause the engine to run hot

Good luck