Thanks to Andy and Angel at Porterfield Brakes for having the 3" Naca Duct that fits to my application with little modification.
After using a Mapp Gas torch to soften up the plastic, I placed the duct against the contour of the aluminum box to get the perfect shape. Hole in box was cut using the template of the duct flange to trace and a 3" hole saw on a drill. Any other fine detail was cut with small tinsnips and a file.
The 3" hole was bored with a 1" hole saw and 14 3/8" holes. Using a file, I was able to smooth out the inside without scoring the inside of the duct.
Needed 400gr sandpaper to finish the inside. After that I used scotch brite on everything for the brushed look.