From what I know the 2.6" Wiard canister comes in two types. 1 is similar to most other canister types and has a tin sided type with a wood sabot and the only ones I have seen have iron top and bottom plates (thicker bottom than top as like other canister rounds). I have a set and Dave Gotter is restoring the round using .85 caliber lead shot (I am a few short and even have a post in the "Wanted" section for some I need, like 4).
The other style is the super rare lead sided and bottomed type. I have a 3.6" Wiard of these and there is an iron top that is separate, but who knows if it is original. I do not have a 2.6" lead one and I don't think Dave Gotter does either.
You might want to eMail him through the forum as he rarely checks in.
Whats odd to me is that your lead top plate still has tin crimped over it. I don't think there is any tin on the lead sided canister version. I may be wrong.
So, I don't think I have advanced the ball much for you, but those are some things I have observed about this odd-sized canister. I am sure yours is right, it is just different from what I have seen and observed.