Why not cut a 1" or 2" hole in approximately the right spot, using hole saws
you already have, then use a nibbler to finish it out? That would work for
a steel hood, but a sabre saw could do the final cut in a plastic hood. You
make the final cut to be exactly in the right spot.
I don't have any experience with a nibbler.
The hole saw worked quickly and made a clean cut. Just a bit of work to accurately figure out where to cut, but doable.