The center hub is a piece of aluminum rod long enough to accommodate the square end of the cable and the screw holding the disc on. Half is tapped for that screw. A hole is drilled at right angles for the allen setscrew that holds the hub to the cable end. The disc is a piece of aluminum flashing. The circle is art downloaded from wiki images - circle divided into 10ths - glued to disc with spray adhesive. Number the gradations 0 - 9 counter-clockwise (disc rotates clockwise). The pointer is made from coat hanger wire.
Remove the speedo, tape the pointer to the cable housing with duct tape. Loosen the disc screw and adjust position of disc at zero.
Not shown - I used a piece of coat hanger wire taped to the front bumper as a pointer to the ground and pieces of masking tape on the pavement marked at 52'-9.5".
Nisonger says it's important to push the car by hand through this distance - some issue with the diff, I forget. Do it 3 times and average the results. IMHO this is a 2-person job so you may have to recruit a "Dreaded Assistant".