76 340 duster overheating at idle

Hard to see from the pics, but looks like a BIG water pump pulley. WP pulley needs to be 10-20% smaller than the crank pulley; that speeds up water flow AND fan speed. Unless the pump pulley is smaller, you will be wasting time & resources trying to fix the problem.
If engine is stock, set initial timing to 15*.

More info here: www.stewartcomponents.com