Advise/Pointers on enlarging hole in hood

Thanks guys. Without cutting a good section of the brace I won't be able to get the circumference I need.

So if the brace is out I guess lowering the height of the motor and getting a taller filter in is the way to go? Any other suggestions for more airflow with current set up?

**I have two hoods. I also have the original hood uncut and painted. It is mint. So I could do a " start over" if required.