I have traced a crude, prototype pattern for the sheath (thanks to @
Funky ), and I present it here, free for all to use.
This should not be taken as a perfect replica, and will certainly need to be tested and adjusted by the end user, but it is a start. This is as close to actual size as I can get given the references. Page size is US Letter; 8.5 x 11 inches. Print at 100% actual size.
Good luck and happy ... digging?