If it's not moving at all, then see if the cable is turning by letting it hang under the dash and then looking at it while moving the truck or rear wheels. If the cable is moving and the speedo is not, that would be unusual.
I've seen many of the heads on the 47/53 speedos fry when the truck is run at highway speeds. It will make noise and then have one last gasp as the cable snaps because the bearing in the back of the speedo head is seized.
Scott's Speedometer in Pontiac, MI has tons NOS parts to repair, rebuild, and properly calibrate these and their work is first rate.
