340 with edelbrock heads overheating

I think that the radiator is significantly cooler is key. You are not getting enough coolant flow. AJ, earlier said, aluminum heads will 'suck the heat out' at idle. If the top end is overheating and you can grab the lower hose and it's a comfortable temp. , I think you have a flow problem.

would consider whether the lower radiator hose is collapsing. The water pump may be sucking it flat.