Cooling issues 69 Dart GTS 340

Do you have your crank pulley and fan pulley sizes reversed in your first post? Looks kind of odd. Usually the crank is bigger than the wp.

is your fan on the right direction? Stupid, but it happens. Don’t ask how I know.....
The pully measurements are what is on the motor. I have 2 different pullies for the crank that I could try. One measures 6 1/4" and the other 7".