I've done a bunch of stuff with electric fans trying to keep my Jeeps cool bumbling around all day at 1mph in the NM desert. Do it right and get an FK-45 controller from dccontrol.com, you make an order and he builds it for you. Takes a little while but worth it.
You don't want the fan to ever turn off completely. That makes the engine bay an oven and bakes everything in there. But you don't want the fan running 100% all the time or you will kill batteries and wear out the fan. The FK-45 can be programmed to run at 10% no matter what, problem solved. And you only need a single speed fan as the controller can vary the speed according to temp. Also, the controller ramps the fan RPM up and down, pretty much eliminating system voltage spikes and sags. This is a must for EFI and good stuff generally.
If you not using a full radiator shroud, get the biggest fan you can find that will fit the radiator. But a shroud is the way to go. I'd recommend a SPAL fan, pure quality. Don't use a cheap fan because if it fails a tow is in your future. A puller will move way more air than a pusher. Wire the circuit directly to the battery, using 10ga and keep the runs short as possible.
