Thinking about going with an elect. fan on my 68 350 hp. No air cond. to keep it cooler. and to cool the engine compartment after the engine is shut down. (heat  soak and vapor lock problems)  

I really like the Dewitts, I have the dual spal fans on my 71 383 stroker, the fans work well. You really should not have a problem keeping a stock engine cool with the standard set-up though. My dual fans shut off when the ignition is shut off, so I am not sure that would be the way to go to cool the engine compartment after you shut down. If vapor lock is a problem, I would look at the fuel lines themselves, a litte heat wrap is a lot cheaper then those fans, believe me.

It is not the number or size that matters, it is how much air they flow.   I always say get the most CFM of air flow possible, especially in Texas.   So compare air flow data, and buy the best.  And you can wire it to run only with the key on, or whenever the engine is hot.

The aluminum radiators usually cool more, not because they are aluminum, but because they have more surface area of fins and tubes. 

Larry

There is a way to wire a temp sensor in the relay ground side that will automatically turn on the fans at a certain temp even if the engine is shut off..obviously this is mounted in the radiator and not the block..so you use 2 sensors..one in the block or thermostat housing. Sounds like a heavy heat wave down your way..
Rich

Lately it has been real nice in the lower 90's.

I have dual Flex-o-lite fans that are in their own shround that fits almost like a factory set up on a C3 radiator. Aluminum radiator with 2 1" tubes running through it and temp sensor on the water passage on the intake. 180 stat and sensor - car did not get above 180 on the hottest days...

Yup..that's thee setup..with a temp sensor not in the block..for the fan operation. It will run cooler with the sensor in the lower radiator area..heat rises..awesome setup.
Rich

I forgot one thing..if you still have the factory alternator with the external regulator you will need to upgrade to a internal style with a 80 amp or so..the fan manufacturer would know the fan amp draw and will tell you how much you need..easy swap though..
Rich

Great, I didn't think about the alternator. 

Be careful wiring that so it will run with the key off. Here in Tucson I have had them start on cars just parked outside, and run the battery completely dry. The weather down here is a little different that up North!