Taking on a 1964 Cuda project

I recently stumbled on to a 1964 Barracuda I couldn't say no to. I'm trying to find the best way to modify the rear quarter wheel openings like this 1965 gasser I found on youtube. Any suggestions would be greatly appreciated.

Video Link: http://www.youtube.com/watch?v=xQ2IZaKULXM

65 with a. 66 grill