RE: fans in general. The best location for any fan is at the hottest part of the radiator core.
On a conventional radiator this would at the top and on a cross flow it would be closest to the side that has the inlet hose coming off the top of the engine. This is because the greater the temperature difference the quicker heat will be lost. If you are using a shroud that completely covers the core then fan location is less critical.
Puller or pusher? Puller if it fits but a pusher will also work if that's the only option you have due to space. I've never seen any great results by running a fan on the front and the back of a radiator. One of them becomes a blockage to the other. A method that does work better is to have them staggered so they don't blow into each other eg; a puller at the top and a pusher at the bottom and avoid as much overlap as possible.
