Well the 1-1/2" bearing came in and there was no noticeable difference between the 8mm id and the 5/16 id in hand or on the router at 8 to
10,000 rpm. It cut a nice 1/4" slot a 1/4" deep. The problem with using such a big bearing with this application is it doesn't cut far enough into the corners of the box. My solution was undo the dry fitted box and hold each side and each end up to the bit and run it up a little so that a squared piece will fit. I'm not suggesting anyone to do this but for me there was not a safety issue.
Make note "Don't Try This In Your Shop" as stated by others have the exact size bearing to fit the bit and don't hold a piece of would with your hand to make a cut as stated above.
[B“It’s not a mistake, it’s a design feature”][/B]