In the sled cutout file, you should add a plug with a .25 hole in the center. I figure the hole would be cut to the inside of the line, and the plug would be cut on the outside of the line. Insert the plug into the center sled hole, install a .25 bit or dowel into your router, align the router in the center hole, and mark the mounting holes for the router on the sled. Remove the plug when you are done.
This would guarantee that the router is perfectly centered on the sled.