just to add for those looking to do this themselves.
if you can either get the fans as close as possible to the rad, or utilize a shroud to house the fans and attach to the rad, it will be MUCH more efficient then if there is any space around the blades - rad.
look at it like this;
try to blow out a candle from 1' away with a light breath - not gonna happen
try to blow out a candle from 1' away, with a light bread, blowing through a 1' long straw - done
air is going to move as easiliy as it can, so if you direct it through a shroud, forcing the air to move - rad > shroud > fan > engine compartmen, you'll get more out of the fan, or need it to work less.
Insert something witty here...