Dorsey,
What kind of water pump do you have on your small block? I had a similar over heating problem on my SBC 32 roadster and finally traced it to a poor quality "no name" aluminum water pump. Seems that the impeller was installed on the shaft so far away from the body of the pump that it would not circulate adequate coolant in the engine. Took me a long time to figure it out. You can easily check it by removing the pump, and back cover on the pump for inspection.

I now have a flow Cooler high volume pump and seldom even turn the electric fan on even with a "non vented" hood and sides.