I'm right slap bang in doing this to mine.

Bascially you need to create some sort of flow to the rad, through the rad and out of the car.

I have got Naca ducts in the rear side windows (i posted a pic in your other thread), these then feed the radiator (which is boxed in) then the air goes through the rad - and out of a vent in the floor. The trick is to create a windage tray under the car which scoops air up and flows it across the vent in the floor and 'sucks' the hot air out/pulls cold in air from the ducts creating a venturi effect.

Obviously you'll need to take the thermostat out - add an EWP and electric EWP controller, associated plumbing, a header tank in the back and a swirl pot.