I have a 71 Chevelle ss with a 350 which has the original four bladed fan. I have recently rebuilt the engine and wonder if I should include an aftermarket fan with additional blades. Will a difference in engine operating temperature be evident?

A four blade fan is a minimal cooling device. If you have upgraded your engine to produce more horsepower, you might want to upgrade the fan. A more efficient fan will increase airflow across the radiator resulting in lower operating temperatures, better performance and longer engine life. There are quite a few fan combinations that you could use to upgrade. If you go back into the heating and cooling posts, you will come across lots of different ideas and opinions. My preference for simplest design and the least amount of money and the best performance would be a engine driven fan with a thermostatic clutch and a proper fan shroud. The clutch engages the fan when it is needed and disengages it when things cool down. This results in quieter operation.