66 steering box Problem

[theshortshorttrailer]

Hello all. D here! New member so if this post has been discussed before or belongs somewhere else I apologize in advance.
My first vintage GM Vehicle, 1966 C10 suburban, Needs a new steering box.
Every mail order shop, as well as the Chevy Truck Shop, etc, has only one listing for 1960 to 1966 chevy truck steering box. Bought one from the chevy shop and it is not right. It is the same as one I saw on a 61 truck. I am told a different box was used on 64-66 trucks. Is this true, why are they so hard to find, and if so, where can I find a rebuilt one?? Any help would be appreciated.
"D"