Wow. Do you have both the plates also? Post a picture if you do and can. You and I may need to figure something out as I have 8 of the balls from Vicksburg.
This reminds me of a strange and curiously disturbing story: 2 or 3 years ago a fellow at the Franklin Show dropped a reconstructed canister round which shattered all over. A couple of the balls bounced wildly and one went over the side and landed on a table on the lower level. The dealer who had bought the reconstructed round was (several emotions but the politest to say is "really confused" by this) until he noticed a couple of the interior balls were in fact golf balls painted black. This explained the bouncing canister balls -- I guess someone should've yelled "fore" when the round smashed. I just looked it up and golf balls are exactly 1.68" dia so I think you have an option here for the missing ones ;-)
I know who rebuilt that round of his, by the way, and just to set the record straight of course it was not our very own CanisterD nor any other forum member.