Go to this site. At the end of the next page on the M10 you will see a couple of diagrams showing the inside of the Achilles. The racks are depicted there.
http://afvinteriors.hobbyvista.com/m10/m10a.html
Here is a pic from my almost completed, modified Achilles:
See Sherm - it's still coming.
These rounds were hand made using styrene rod that was carved and sanded down to the correct shape. The collar was made up using thin fuse wire loops. Hope this helps.
PS welcome to the forum