Well here is what i did... Take a permanent marker and make an outline of the vents. Make sure you have them where you want them. I think used blue masking tape and taped around the marker. I cut it on the inside of the marker line. I needed to do a little more trimming but i figured a little more trimming is better than the hole being bigger than needed.

I covered the motor also with a towel. I didnt want any debris from cutting them to be able to get into the motor. I cut mine with the hood on also. Its not too difficult. If you can trace a line then you can do this. I used a cut off wheel on a die grinder. I kept the piece i cut out so i can put bolts through them and put them on during the winter.

I also sealed mine with Blue RTV. Dont know if it makes a difference but i did.