Here is a picture of a 383 stroker rotating assembly. Diamond piston, 440Source rod and a 413 crank that was in process of being turned down. If you look close you can see the spud mounted on the crank flange for the lathe. Using an aluminum spud allows the lathe chuck to grab hold of something solid rather than trying to grab on the flange. On the other end you use a live center that goes in the nose of the crank. Runout is usually less than 0.001 when using this setup.