If your hardware store has hex stock that might work... But I think maybe welding a 5/16 allen wrench with the 90° cut off on a peice of straight stock. The hex has to be hardened steel.
Some machine shops carry 5/16 hex stock. You will need about 16 inches of it. Get them machine off the hex portion off the shaft 1 1/2 inches either side of center. (three inches total) This will stop any wear on the intermediate bushingwhile priming. And yes it doesn't have to be hardened steel for this application.
