UPDATE January 2016 - I successfully created 2 inserts for the Dewalt 7491RS saw to be used with the blade guard and riving knife that came with the saw.  However, due to the horizontal movement of the curved riving knife when the blade height is changed, each insert can only be used for a specific height range.  I made one insert for cutting 2x4's and plywood.  The other insert is for the maximum blade height (I think 3.5 inches).  If anyone wants specifics about the slot length needed for the riving knife on this model saw just post a question or comment.  Unfortunately, you need to cut the slot very close to the back edge of the insert plate in order for the riving knife to lock into place under the saw table.  But with patience and a fine touch you can cut the slot to work without the need to cut the slot through the back end of the plate.  I really like these plates.  The side adjustment screws make it easy to get the plate to fit snug and the top screws let you angle or level the plate as desired.