Here's a good read that will sum it up better than I can: http://reischeperformance.com/WhyLowTemp.html
Probably would be better to just use the GT hood. They have all types of extractors that replace the stock ones depending on what you want. All the work/cutting has been done. If I stumble across a 3X Yellow one locally I would upgrade if the price was right.
Well call me nuts...but for me, I am not that much of a fan of where the stock hood extractors are. Besides...if you look at the wind-tunnel tests, the laminar air-flow is still attached before it hits the windshield. I think the the stock hood extractors are too far forward and I might get more effective heat extraction if I put them in the center and more towards the back. I plan on going over some figures with a friend of mine who is an aerodynamic engineer and see what he thinks.
If you look at the GT350 and GT the heat extractors are in the front of the hood, the air-flow across the hood back to the windshild then is sucked under the hood and flows to the front.
And that is another reason why I don't like the design...its too inefficient and cumbersome. My hope is this would streamline the process. In addition, some studies have shown that if you place the extractors just right...radiator efficiency can be improved.