What I did with mine was that I made a pattern of my original metal blade insert. I made it out of MDF. Bandsaw to rough it out. Sanding belt to bring it into shape and into final form (smooth). I had drilled the hole through it oversized, and put in small pieces of tubing to use them as drill guide bushings, to drill holes into the insert blanks. I had cut the slot through the "pattern" using a smaller diameter blade to start it. Then finshed off with a 10" blade.
I use double sided tape to attach my insert blank stock to my pattern... That way I could take that to the band saw and rough it out... Use a router and a pattern bit to take it down to size. Sand it smooth. Drill the holes. And while still attached to the pattern, mount it in the insert throat with long screws, to bring the blade up throuhg the slot in the pattern to start the slot in the new blank.
I remove the pattern, then run them through my thickness planer to get them to a finished thickness. I usually make about 4 inserts at a time. On that Rockwell, I also use 6-1/2, 7-1/4, 8" blades and 8" dado's. So have inserts made up for those sized blades for various kerf sizes.
One thing I do extra to them is to add a wooden splitter to the rear of the slots. What I do is to extend the slots to the rear and glue in a vertical wooden shim. This is just a safety thing to try to prevent kickbacks. And I'm telling you it does work.