The ebay shims may work, but as mentioned they may be too thick, then you wasted your money.
In the book "Chrysler Performance Upgrades" by Frank Adkins, on page 22 he discusses reviving cone-type sure grips. He recommends cutting 0.080 off the ends of the cones, then measure for required shim thickness using a feeler gauge behind each spider gear. The hardware store will sell steel sheet stock. Then cut out your own shims and install.
The last one I did this process to, the cast iron case where the cones seated had hard areas of the iron casting that were causing gaulling of the cones. So eventually the cones would completely wear out. I repaired the cone type sure grip, and sold the pumkin. Then I bought a 742 clutch type rear diff where mopar still sells the clutch packs new; don't forget to add the mopar lube additive for clutch type sure grips.
Machining and shimming does extend the life of the cone type sure grip, but it won't last forever.