I am curently working on a vintage project, Short story is this is a 1964 CJ5 made by Kieser Corp and the engine is the 231 Buick V6 a complete swap. The engine is out of a Buick Skylark 1975-77.  Engine fits fine but with the 15" flex fan in place I can not mount the radiator without hitting the fan.  I would rather there be a flex fan on there because I don't know or have heard of the electric fans being all that.   There is a spacer that goes between the fan and the upper pulley wheel, is it necessary that the spacer is there?  Any info will help greatly! The sooner the better.    

You should have a minimum of 1 inch between the fan and the radiator. You dont need to use the spacer, just make sure you buy or make a fan shroud so the fan blades are half in and half out of it.  

Neither Flex fans or electric fans can compare with an engine driven clutch fan that is properly shrouded.

You MUST have have a shroud!! Minimum 1" and no more than half the the thickness of the fan should be inside the shroud. The clearance between the shroud and the blades should be 1 to 2 inches.

Put the effort into the engine driven clutch fan.
Otherwise you'll be fighting cooling issues and be back to looking at it in the future.  

the electric can help in slow speed driving situations when then engine is laboring like cuttin a trail in snow, If you figure you must have a electric get one that was oem for a system of the same capacity as you have, the aftermarket units are mainly for auxilliary usage.

some cherokees have only electric fans.... they also have cooling issues.  

For the best belt-driven fan performance I go with these.
http://www.flex-a-lite.com/auto/html/race-fans.html

If you can fit 'em. They move massive amounts of air at low and high RPM but make a lot of noise and rob some power. Good for Jeeps with cooling problems though.  

So nobody really likes the flex-a-lite fans on like a '99 TJ?  

A flex fan is designed for high-speed use. Mostly for cars and hot rods. It flexes at higher RPMs, moves less air, and assumes that vehicle speed is increased when RPM is. When you are wheeling or towing this is not always the case. Imagine crawling up a hill in low, revving the engine. Very little air is being pulled through the radiator and there is no road speed to push it through. No Jeep should have a flex fan unless it's a drag Jeep or maybe a sand race Jeep.