First let me say Welcome!
Next let me ask, Is this the same saginaw box that went into trucks up to '72?
Would it be the type that serves as the rear engine support with a rubber mount on each side? Hmm, now that I'm thinking about it that may only be the bell housing.
Annyway, If this is true you may also have luck finding this on the 67-72 parts board as well.
Keep the shiney side up
Denny