Found a pic from when I was doing mine, it may help
You can kind of see how/where I cut the centers out, I used the center opening of the back side /inner wheel as a guide for my plasma cutter and just followed the circle
Also not sure if you've already bought the parts but here is who I used, at the time they were a good bit cheaper.....I am more then happy with their product. I did use trailworthy for my inserts.
http://www.cmperformancemachine.com/Pressed-Centers/
You can kind of see how/where I cut the centers out, I used the center opening of the back side /inner wheel as a guide for my plasma cutter and just followed the circle

Also not sure if you've already bought the parts but here is who I used, at the time they were a good bit cheaper.....I am more then happy with their product. I did use trailworthy for my inserts.
http://www.cmperformancemachine.com/Pressed-Centers/







