We bought some pieces to act as spacers and square washers to clamp down on the plate using the existing nuts and tie rods.
But the pieces that we ordered weren't the right size, nor even uniform in size. So we had to cut and then sand them all down. New undergraduate intern, Channing, helped with this process. First he carefully sanded each one on the belt sander, measuring after each sand.
And then he installed the pieces and washers to the rig. I can't wait to see the improved stiffness measurements!