any electric fan that will fit flush up against the core is fine.
If you want to do it properly, you should probably set up a thermo switch. A switch that tells the fan to go on when it reaches the desired temperature.
Or you can do it the super easy way, but more annoying in the long run, a flip switch on the dash somewhere to turn it on and off.
The thermo is better, as it switches on automatically when the engine gets hot. I'd recommend this way.
The switch is easier to install, but you have to look at the temperature gauge all the time, and if you forget, your engine dies.