Nice haul! A thin nylon or mylar washer would work well. Mylar is usually used as a drafting film. Neither will wear very much so be careful not to make the pinning too tight.
Aluminum, from my experiences, is a nice material. Howsomever it will show every deep sanding scratch til you have worked reversed diagonally up the grits to a polishing grit. then you may have to drop back a few levels to get the scratches that show up then.
Attachment 228813
If you look carefully this was at 2K grit. I had to drop back a couple levels to get the barely visible scratches out.
Have fun and don't get discouraged by having to go back a few grits more than once. I have worked aluminum and other soft metals most of my 50 year career and...I still had to go back more than once. The I could go and carefully polish with a new buff and fresh polish. By hand with an automobile polish, or Filtz, or Simichrompoly will do also and less chance of showing polishing feathers like on the right lower part of the top one above.
poly will work also.These are hammer formed but your solid ones will finish the same way.
Have fun!
~Richard