Hey Todd,

From my experience, there doesn't seem to be an easily explicable rhyme or reason why each car comes from the factory the way it does. The front fan is usually an auxilary unit that's activated by the a/c since it's attached to the condenser.

I can't tell from the blur in the picture but those ports look to be cooling flaps. Zionsville Autosport offers the same feature on some of their radiators - basically they just open up at speed to increase flow. The different routing may not be more efficient, it may just be out of necessity to accomodate room for everything since the motors are different. (Although i've never looked under a 4.6 hood to compare so that may or may not be the case) Perhaps it may have something to do with the 4.8 bumper having larger openings? Again, just hypothesizing..

Turning to Dinan probably isn't the wisest financial decision. You could certainly have a sweet Ron Davis radiator custom made for the same $, if not LESS that would probably be a better solution to your needs. You could also probably delete both fans and add an electric one from Spal similar to the 4.8. (I've done this to my M3) This would free up some space behind the bumper to add an additional/larger oil and/or tranny cooler as suggested above.