I have received a great deal of helpful advice on how to finish these from much more experienced gentlemen such as Pete Young and Rick Parkington. The constant theme appears to be that sanding these down is "knuckle-busting" work. Fortunately, I found the right tool--a Black and Decker palm sander. It spans several corks and lets me slowly sand them down evenly.
chainwheel being sanded
In similar fashion, I have been sanding the friction plates. It's tedious work requiring frequent measurements to ensure that the plates are close to the same thickness. My concerns are starting to build as more material is removed. If I leave the cork too thick, it will be be difficult to adjust the clutch. Furthermore, cork expands as it heats impacting clutch performance to the point that some advocate leaving the bike in neutral while at a stop. This violates the Motorcycle Safety Foundation's rule of staying in gear to theoretically avoid getting rear ended. Good theory but I don't know about the practice. If the corks are too thin then reliability goes by the wayside. We'll see how this progresses.