[Gav]

Why duct it out?
The hot air from the radiator gets ducted out over the bonnet so the only hot air is from the exhaust.
If your intake was in front or on top of your engine it should be ok.
You could open up the back of the bonnet bulge like an original to introduce cool air in the upper portion of the engine bay if you need.
I'd wait until you have been running it and see how big an issue you have before re engineering it.